Warning - this is intended to be long, complete, and detailed.  

Preamble
Much love for the Bullpups and Bullpup concept.  Have an AUG for close to a decade.  Have an MDRx in 6.5CM (because I also have a big admiration for the 6.5mm family).  Have run and handled Tavor's.  Even had a chance to fire an FG42.  Have a Bullpup 12 ga that I love.  Have a bullpup SBR'd 22 even.   Haven't run the Hellion yet.  

While I love bullpups for the efficiency, there are a few Wishes for bullpups I have:
1) Lighter
2) More accurate (none are what I'd call SUB 2 MOA all Day - whereas even the cheapest AR15 can be; 1.5 MOA and I'm happy.  My $2500 MDRx can't do that, or even get close)
3) Better trigger (actually the AUG with the upgrades and the MDRx factory are both decent, TBH)
4) Ambi friendly (not a HUGE deal, but I one wanted to do a 45° offset on the AUG, which is a really bad idea where that puts the ejection port!  MDRx gets there, though)
5) 6.5 Grendel  (MDRx tries with 6.5Creedmoor.  which WOULD be great, if it were also a 1.5MOA gun, which it's not).

RDB satisfies # 1,3,4 right out of the box, and has potential for #5.  We shall see on #2, but the reputation isn't good.  And it's well.. KelTec.

Acquisition
Finally had chance to pick up a new RDB for cheap.  I'm not poor, I could get an RDB whenever I wanted, but since already have the AUG, wasn't going to pay full premium price for a duplicate 5.56 3 MOA gun.  After a few years of looking, finally got a new one on sale for CHEAP.    Also, I recently got an ACOG in some horse-trading for basically free, so it needed a rifle of course!  Also, bear in mind, if RDB were offered in 6.5 Grendel and accurized to 1.5 MOA and holds zero; I'd pay $2400 for it without complaint; but they don't so that's why I was fixated on buying it cheap.

So this thread is an attempt to follow the progression of this RDB, akin to other logs I've done.  

The first post is going to be background and setting.  And assessment at the "unboxing"   Most of it with many of things others have said, some of it maybe not - just my own take as a non-Influencer.

Unboxing (just saying that word sounds lame, but here we are)  So here's what I got:
A stock new-in-box KelTec RDB, with a 20 round PMag, an empty chamber indicator, a sling and hardware, some stickers, and a manual.  I looked close for signs of usage, firing, and handling, and saw none, so even though old, I guess it really is New Old Stock.  This would be the 17" unit with the plastic furniture.  Running the Serial number, it's only unit 2500 or so, and made about 6 years ago, apparently.  The good news is apparently it still has mostly the latest-gen features and updates.  So this one has the latest gen bolt, firing pin, etc; as far as I can tell at least.  So I guess they started doing most of that before unit 2500 at least.  The barrel is marked 5.56 NATO, and everyone says it's 1/7twist.  Comes with A2 FH, and an interesting and different flat-nut in lieu of the crush washer; that's kind of clever of KelTec.

File photo -but this is what I got:


First impressions:
-The KelTec plastic furniture and their signature grid pattern is just FUgly.  Will work on that.  AUG is much more attractive in lines.
-The gun is indeed light.  I like how thin it is in the middle, making it double easy to one-hand hold there.  Notably lighter than the AUG.
-The trigger is everything they say - it's just amazing, and has a nice 2 stage break.  Geisselle isn't in trouble here, but it's pretty good.  Even after almost $200 in AUG trigger parts, it's still better than a tricked-out AUG trigger.
-I hate the mag latch, and feel like that is going to be very easy to bump and accidentally release.  I may do some mods to make it stiffer.  A slighter harder and slower mag change is far less relevant than "where's my mag?"  People value shaving fractions of a second on the mag change of a 30 round mag far more than I do; especially in relation to keeping the original mag secure.  I like the AUG mag latch better.  In testing, I found it very easy to accidently engage and drop mags (though in actual usage at the range - less so; it actually wasn't a problem - so far; we'll get to the first-run range testing in follow-up posts)
-The balance is nice.
-The gas adjustment on mine has 19 detent clicks that engage in rotation, with a touch overage I can do in each direction.  Apparently it opens more as the plug rotation drives it forward (this felt backwards to me, but OK).  TBH, 19 clicks is a lot of adjustment, but OK, nice to have the option.  The AUG 2 position gas adjustment is insufficiently adjustable to my needs, and is still overgassed even with a Suppressed plug on Suppressed (though that's particular to my AUG's BBL, as a friends 16" on normal is softer than my AUG on Suppressed setting still)
-Fit and finish blah blah, is all good.
-This gun will support doing the HK-slap, with the handle extended when you manually lock back for that easy slapping - all I need now is a turtleneck and a beret.  Most importantly, the parts involved are metal-on-metal; unlike the AUG which in theory can do the HK slap, but don't - as it's plastic on sharp point metal, and you'll chew your plastic part to unusable (for locking) trash very quickly if you try doing that on an AUG.  That said, the RDB handle sometimes goes up into that lock position a bit too easy, so something to watch for in manipulations, where you might think the mag catch of an empty mag you had in there while racking the bolt manually is what's engaged, when it's really the charge handle went up into HK slap.  When locked back, the handle won't go forward of its own accord, so you don't actually know right away, until you manipulate it some more. No big deal, just a usage nuance.
-The safety is kind of different, maybe it's better.  It's an AR position and usage, ish, but the positions are a bit different.  Maybe it's better, but it's different.  It works.
-The top rail is good and has a lot of real-estate, but I kind of wish it came back more, so as to better host a 45 degree Red dot option - though see below on that.
-People act like the barrel is really thin, but I don't think so.  I think it has a pretty good and efficient contour actually.  It's not a heavy barrel, but I don't think it's any thinner than an A2 profile under the handguards, or at least, not by much if so.
-The factory bolt-release button is small and quite stiff on the new gun.  I suspect this will break in, and am running it dry for now to wear in the parts, and then will lube it well, and we'll see.
-I don't know what the barrel finish is.  Maybe malonited, maybe not.  I don't think it's chrome lined.

Mechanically, it's a clever system.  As most folks know, it's a short-stroke piston with non reciprocating handle.  Bolt is a standard AR concept of little lugs and rotation, with a longer cut kidney hole in the bolt carrier for the cam pin, for softer operation.  My firing pin has a spring in it, apparently the later units do not.  Apparently it doesn't matter either way, so hey, I'll take the spring then.  

The trigger is very clever.  Where most Bullpups use an extension rod to trip the actual fire-control trigger pack back in the back, this unit trigger trips the sear directly via the trigger, which is how they are able to make it so good, and they have some exaggerated length parts to make it all work.  It's actually kind of genius.  With the rear-bottom ejection, the hammer is this goofy long thing that goes back behind the ejection port.  So to have a reasonable lock-time for the long travel, it has some pretty impressive springs to do it all.  Which I suppose explains why sometimes these firing pins can break ;they must get whacked the bejusus out of.  This is one gun I won't be dry-firing a lot.  I don't know what the actual lock time is, but it certainly was fast enough to appear no different than any other gun from trigger-pull to fire; which is to say instantly, as far as any operator can feel.  Oh, and there's some videos out there of someone getting double fires - which apparently happens if you pull the trigger again while the gun is cycling.  So... don't pull the trigger again while the gun is cycling.  TBH, I don't know if I could do that if I tried, but he's right, it'd be better if it didn't do that.  It's not an item I'm having issue with.

Internet photo:


Parts - and system
The barrel is connected to the top rail where the sights go, via two blocks on the barrel, one forward where the gas system is, one in the rear, forward of the barrel nut and barrel extension.  In theory one could swap out barrels reasonably easy by driving out the two roll pins and pulling out the barrel; and bolt easily as well with a different one (i.e. for Grendel or 6.8, etc); though nobody offers that option, unfortunately.  Considering my own RDB is unit #2500; I can guess there's my answer as to why (though I think they are into the 10's of thousands by now?).  The barrel is of unique dimensions and contour, as is the bolt, so there's no "making due" with any sort of AR parts here.  In theory, this is kind of great, because the barrel/sight rail are basically the heart of the whole gun, and are intimately connecting the sight to the barrel.  which SHOULD be great.  Buuutt...

TBH, I suspect (but don't know) that this approach is actually the contributor of the RDB accuracy complaints.  Folks blame the barrel being too thin and whipping, which I'm not so sure.   I actually like the barrel contour and dimensions and think they are fine.  I've had thinner barrels shoot 1 MOA just fine on an AR.   I question if it's really the fact the sighting rail is secured by two roll pins to the barrel, and the barrel is obviously not free floating.  Not only does it have the stress of two attachment points on each end, plus the bolt at the breach, but it also has the handguard connected to the forward point.  As the barrel heats up, and as variable forces are put on the forward handguard, and the gas-block which is what the handrail is actually mounted to and in contact with heats up and just does it's jumpy thing; the mounting rail to which the scope is mounted is going to have variable forces on it too.   We'll get into accuracy testing on my next post; with some good results actually.  

Being new, I scoped the barrel, which looked even, sharp and good, with a good throat and crown, and rifling overall.  The chamber itself has a little chatter in the based, but that's not important.  It was of course clean and unfired.

For initial starting measurements at 0 rounds:
Measurements (we'll update as we go)
Headspace: is 1.4666 < actual < 1.4676  Which is right at the top end of a civilian 223 Chamber, and is good.  For reference, my AUG headspace is much longer and right at the top end of a 5.56 chamber (barely).  We'll get to that, but I consider that about ideal for the RDB.  Big enough not to be "match" chamber dimensions with the problems that come with that when imperfectly resized reloads are being used, yet not so sloppy as to have exasperating head-separates like a sloppy 5.56 full length chamber can do.  (they do that with 5.56 military guns to be more reliable when heavily fouled, and factory GI brass will stretch to that dimension just fine on the first firing).
Throat erosion: Using a comparator with a Nosler 80 gr bullet in the rig, the OAL to hit the throat with an 80gr is 2.482" OAL.  that number itself has little meaning, but it's the reference number used to monitor throat erosion as the barrel ages and wears.



Mods:  Before even firing it, I did a couple things:
-I replaced the muzzle device with a Brav0 BCM break.  I really like that break, as it is a 45 degree baffle, so not nearly so brutal of a blast - which on a bullpup or SBR, matters -  In this case, it worked great, with essentially no noticeable blast issue while shooting it.  I went with a crush-washer and a spacer, as just a touch lighter and shorter than the KelTec nut approach.  (I have a bias to keeping my muzzle devices as small and light as possible).
-I put an old Uncle Mikes or such rubber slip on grip on the pistol grip.  This is one of those rubber textured gigs with slight finger nubs.  I didn't really do this to improve the pistol grip, so much as to cover the hideous KelTec grid pattern texture they love, that just screams Ghetto.
-I put the ACOG on there.  Much pondering on the mounting systems and options.  I ended up taking off the LaRue mount, and actually replacing with a primary Arms mount for now, to be smaller and free up more rail space to potentially install a 45 degree offset red dot; as 4X is a lot of X for CQB with this gun.  Honestly, i'm not sure if I'm going to keep the ACOG, or just go back to the 2.5X CQB Primary Arms rig, that all my other guns run; to keep it consistent.  You can CQB well enough with 2.5X.  but with 4X....  we'll see, the ACOG is on it now.

Mods in progress/ on the way
-I ordered a 45 degree offset mount and red dot; of which I'm not very happy.  They don't fit together, so something will need to be returned, but also, it really sticks way way out there further than I was figuring, and I'm not so sure I like that.  I may abandon this concept; I haven't decided.
-I ordered, but haven't gotten yet, the Lucky Irishman Rhino RAPTOR aluminum handguard.  Mixed emotions, it's $200 by the time in hand, which is about a 30% price increase above what I paid for the gun (got a SWEET deal on the gun), but will replace the hideous look of the KelTec plastic handguard.  I will say, the plastic handguard does actually work, and on a 50 degree day range session, was quite comfortable in my bare hands; which aluminum won't be.  So.. we'll see.  For now, I'm running the stock plastic handguard, because that's what I've got.  Some have insinuated the LuckyIrishman can improve accuracy, as well as be a heat-sink and radiator.  We'll see.  If it improves accuracy, that will be money well spent.

Looks to be a great thread coming.

Looks to be a great thread coming.

Had chance to do a range session this weekend.  Went through 400 rounds of various ammunition ranging from light 50 gr ammo loaded mild, to heavy 73 gr ammo to 77 gr Lapua match ammo.   Will update with results and findings..

I will say this, the complaints I see about heat in the RDB didn't show up at all with me.  At no time did it get notably hot; certainly no more than an AR or AR barrel.  I was expecting the gas system to cook hot, or the take-down pin to get hot and burn me, like so many complain.  That didn't happen - at all.  I wasn't heavily rapid firing it much, but I shot it quite a bit all the same.  I'm wondering if theirs were overgassed, and so over heated?  Don't know, but it was a non-item for me.  In the next few weeks I'll do some action shooting with it, and run it - this outing was focused more on getting started with it, and doing zero and accuracy testing, getting used to the adjustable gas system, and seeing what ammo it likes.



Also learned that ACOG's really do have a learning curve.  My recently acquired unit is quite old and was mostly abandoned unmaintained for probably 20 years (the tritium is quite faint now, though it IS a real unit, and not a knockoff).  The notion that you have whack them upon adjustment to seat the prism, was something new.  This won't be a "click to target" scope usage, I'll say that much.  Once it's set, it's a hold-off's to target, scope!

And also brought a spiffy new little rig with me, one of the new Garmin Xero's, that wasn't cheap - but completely blows away the LabRadar experience; which I was able to sell to subsidize the buy.  All the rave's people have on these rigs are basically true - it's stupid easy to use and works every shot without even trying, though the App kind of sucks, IMHO.

The complaint comes from the captive pin that holds the handguard in after long strings of rapid fire..Since most of us dont do that (Many due to range rules)..Its a non-issue

Yea, makes sense.  I was surprised mine never got hot.  But as you say, I wasn't doing mag dumps.  I will in some follow-up outings, and we'll see then!  

Also, the handguard is such that it takes considerable effort to try and physically even touch that pin while the gun's assembled.  I have to jam my pinky hard and just so, to barely touch it.  Maybe they tweaked the design at some point, due to pin-burn complaints from earlier units?   Even if that pin were smoking hot, it still wouldn't actually touch my hand even if I'm holding it right there, with the handguard I have.

I..it might have been changed..But like you my RDB (with a double digit S/N) also has that pin recessed into the handguard and it is difficult to touch without (as you say) "trying"

Update 12/28/2023 total round count: 25.   (gas adjustment on new rifle, so some failures as normal and expected)

Took the cleaned and oiled new gun with the ACOG on a LaRue M110 QuickRelease mount that came with it, up to the range for a 15 minute sight-in / gas adjust session.  The gas system has 19 adjustment notches, and I will label as -X as the count of notches from the last notch that is fully open.  (i.e. fully open notch = -0)  

Running my normal baseline 55 ball load.  For the reloaders out there - this is a warm charge of 23.5 gr LT32 under a Hornady 55 FMJ, for a nominal velocity the same as Wolf Gold (a very clean relatively warm load that gives about 2950-3000 FPS out of a 16" BBL with good basic accuracy.  This is a fast powder, so in longer gas systems, tends to give a little more pleasant and mild gun recoil since the port pressure is actually on the low side, even though fast velocity - it's my favorite general purpose 55 ball load.  

I went in with a gas setting of +4 (which is -15 from fully opened).  Gun didn't cycle at all.  So how hard is it to clear a "jam" from an RDB?  Took it up a few more notches at a time, and it wouldn't cycle until I got all the way up to almost fully open, at the -1 setting.  This surprise me, since I thought for most people their RDB's are much more closed off to cycle, and this one needs basically fully open. Which is fine.  Also, since during this process of figuring out settings, the gun will jam getting you there.  And so learned how to clear jams in the RDB - a topic of concern on every Bullpup review ever.  It was a total non item - rack the bolt, shake the gun, rack the bolt.  off you go.  Also, I didn't have to break it open for anything, but if you do - the  RDB can be hinged open quickly for access and maintenance by just pushing the captive take-down push pins.  I think you only even need to do the back 2, to do it.  But that didn't come up.

In processing to get here, also tried zeroing the ACOG, which was not successful as it was WILDLY off in elevation, by 30 or so MOA.  Tried dialing the knobs, but there were so stiff, I feared breaking something.  

Once I got the RDB gas system  dialed in at -1 gas setting, the gun ran 100% and I ran a few 5 shot mags through it without any mechanical issue.

I will say, the recoil of this gun is very soft.  much milder than my AUG.  Between the soft recoil, the lighter weight, the exceptional trigger, and the bottom eject system so that the gun is effectively sealed, with no gas venting back at you or blowing out the sides or blasting out of the gas system right up by your hand, it was a very pleasant experience.

I touched the gas system and other parts to see if anything was getting warm in any odd ways, and didn't feel anything.  Also, running the BCM muzzle break worked out very well, with no noteworthy blast behavior.  If anything, it felt as mild or milder than a 16" AR with the same muzzle device - which is further away - so that is is probably just in my head.

So far I'm really liking this gun.  But on this trip, can't comment on accuracy. But a very pleasant gun to run.  The downward eject was tidy, as all my brass was right there.  

Rounds fired: 25.  jams (about 4 or so dialing in the gas).  Total round count on gun: 25

Keltec built up a nipple surrounding the take down pin to address the burning issue. You have to actually stick a finger tip in to touch it now. You can see where they modified the mold here.



The gas system is genius. Heavily influenced by the FNC.

Be careful doing the HK slap. It wears fast.

Pull every shell screw and thread lock it. A few of mine weren’t tight to begin with.

Do not cycle these while empty anymore than you have to. The charging handle catches on aluminum and it will damage over time. I did the HK slap a bunch and it’s gouged the catch face to the point it makes my charging handle stick.

I prefer the factory MLOK handguard to the aftermarket options. It retains the quick takedown and appears to be a bit slimmer. I don’t know if Keltec changed the design but mine is super tight even before painting contrary to rattle reports.

It gets hot. There’s no way to avoid it. Run rail covers if you get an aluminum handguard.

Mount the optic as far back as possible. The optic rail moves as it heats up and Keltec even advises against using thread locker on the screws up front because of it. Keeping it away from the front will reduce stringing.

My mag release is stiff. So stiff that I end up with a bruise after a range trip if I do the thumb bump method. I now finger pinch.

It’s a crazy fun little rifle. Much more pleasant to shoot than any other bullpup I’ve gotten my hands on.

Keep up the updates! With the cost of ammo, how many other 5.56 guns I have, and limited free time I don’t get to shoot mine as often as I like. Will be watching this to see how it works out for you.

Attached File

I went with the LuckyIrishman (Rhino handguard). Took Keltec some time to comeout with theres and Richard has gotten my business for every bullpup since.

Looks like a small amount of material was added to the smaller "top" lip. This is from my handguard and its and early pre-production model

12/30/2023 Update : 250 rounds fired (275 total).  A few jams while experimenting with gas adjustments - other wise no jams (er.. no jams with the RDB that is - read on).

Per the above photo, I brought out the RDB, the AUG a Chrony, And about 20+ different magazines preloaded with different ammo between the two guns.  Todays outing focus was mostly on 100 yard paper with some targets at 50 and 200 yards.  

After spending a few minutes setting steel and about 50 paper targets for the day at the different distances, I then went back and unloaded at set up at the bench on this cool but pleasant sunny 50 degree day.

First order of business is to figure out if I'm going to stick with the ACOG or not, and I brought a spare Primary Arms 2.5 CQB just in case. All my other guns run the 2.5 CQB as my standardized glass, so going different with ACOG is kind of mixed emotions, that and I still think 4X is a lot of X for a gun that might be CQB usage too...  Donno.  For now I'm running the ACOG, but did switch to the smaller and less rail-space consuming PA mount that comes with their 2.5 scope (that works on ACOGs).   But if this is going to work, I have to zero that ACOG.  So at 50 yards, it was impacting in the dirt at the base, like 3+ feet or so below point of aim.  I finally said F'it, and lightly used a multi-tool to see if I can twist the stiff dials (but careful like).  they quickly loosened up, and to my suprise, had enough clicks that I was able to travers that sucker all the way up to impact.  

I then went out to 200 yards, and zeroed it with my 55 ball, which is my reference distance and round I zero essentially all my 5.56 guns on.  Accuracy was... ehh... well, still warming up and figuring out the scope at this point.  

Over the course of the day, I fired mostly at 100 yards, and some at 200.  I'm still compiling my data and performance activity, but did find a few trends of note.
1) The RDB is easily as accurate as my AUG.  But it still wasn't very accurate.
2) The RDB is a much more pleasant gun to fire, than my AUG.
3) The only magazine that had issues with my RDB, was a GI C-Products aluminum mag, where that sucker just did not want to securely latch in.  All other mags (Lancer, GI 20s, PMag, ETS mags - all ran great).
4) There were no accidental mag releases.  Even in handling and things getting bumped, there were no accidental mag releases.  But most of this was bench shooting today.
5) The new Garmin GPS is completely F'ing Awesome - and I'm so glad I dumped by LabRadar to help pay for it.
6) The ACOG green illuminated reticle is awesome, but in some settings kind of hard to see that green.  Though the ACOG glass is ridiculously good quality.  That is some amazingly sharp clear glass.  While I like my PA 2.5X, this glass is better.
7) When shooting from a bench with a side-cutout for your chair - placing a box on the ground below the gun a tidy way to get all of your brass collected nice and easy.
8) If I could only have one bullpup in 5.56; which would I pick.   man, I have to say, as iconic as the AUG is and as much as I like it, I'm going to have say, that RDB was basically better than the AUG in every category - and in particular in just how pleasant it was to shoot and the overall user experience.  I will say, I watched a few of the recent Guntube "Influecner" video's of late that came out in the last few months with tacti-bro's running several bullpups at once, and in all of them, they all picked the RDB as the best one.  I kind of see why.  
9) the 17" RDB barrel was equal or greater velocity than the AUG 18" Barrel.  I suspect this is to do with the HUGE gas port venting out the side of the AUG; because at Steyr, it's better to run way too much gas to the gas system, and vent what you don't need; than it is to just constrict how much gas you vent, to just what you need.  (I once layed a business card across that vent port for grins in my AUG, and it shredded that thing into confetti)  Where RDB basically uses all the gas it takes, and vents very little to waste and lost velocity.  it's also drawn much further down the barrel, where port pressure is lower.

I doubt many will study this, as that's quite a data dump.



In general, neither gun shoots very well, with 3 MOA being a good group, with some ammo and on some strings.  It appears to do better with lighter ammo, and for whatever reason both guns really like that 55 gr HPBT.  Historically the Hornady 55FMJ Ball lot will shoot 1 MOA in a National Match AR, so that bullet CAN shoot.  And it does good in other AR's, but only decent here in the bullpups.  The 50 gr JHP round also went well.  The national match competition 77 gr Lapua load, did mediocre in the RDB, even with the reduced gas setting.  In general, -1 (almost full open), was needed for much of the ammo, and the hotter heavier ammo was able to throttle back a little bit, to -3.  You can sort of feel when the gas might be able to be throttled as you shoot - or maybe that's in my head.


Here's a photo of a casing out of the RDB.  Note how it has striations markings on there - almost like it's fluted.  I don't think it is fluted, but it's interesting.


For failures, the AUG had one broke shell, though no broken shells from the same lot of ammo in the RDB.  this has to do with AUG's sloppy chamber.  this isn't common or frequent, but it has happened before.  



Brought the RDB home and pulled it apart. very little wear or fouling to show for it.  Maybe a slight wear on the gas piston.  

Total round count: 275 rounds on the gun.

I’ve had my RDB for a couple of years now and agree 100% with your assessment. The weakest part of the design for me is the cheesy mag catch - if someone could come up with a more secure design I’d be over the moon. A militarized RDB  (heavy duty parts, better mag catch, ditch the screws) would be an outstanding military weapon that I’d love to see KelTek license to one of the big military armaments manufacturers.

Have you tried the PA 2X? It’s the optic I eventually plan on putting on mine. Thought I read somewhere the 2.5 was going to be discontinued soon but couldn’t find the info.

It’s hard to explain but magnified optics just feel weird on it. I tried a LPVO and a PA 3X Microprism but struggled on follow up shot speed. I can throw the muzzle around easier but I think my stability off hand is reduced with the bullpup. Something about it is just awkward trying to be accurate.

A few of the targets with analysis, to show group sized of the RDB; and some of the AUG for comparison.  These would be some of the targets used in the above posts Excel spreedsheet.


Some ammo the RDB liked and group well, some meh, and some not so good.  Also, the RDB seems to have a flyer in every group, which lots of people dismiss as shooter error, but I don't think so.  Odd how much it loves that 55gr HPBT.  I'm not sure why it substantially stands out so well, vs the Hornady 55FMJ, which is a good bullet too.  They both are the exact same load.    Even with the 55 ball, It'll hit an 8" gong at 200 yards all day, which is decently servicable, but I was hoping for just a touch better.  

Note most of these images are basically Best Groups of The Day, and a few of the pics are the more representational.












Here's what the 17" barrel looks like on comparsin to a 16"Faxon GUNNER profile.  The RDB is actually thicker.  


-----------------------------------------------------
For comparison, here is the the AUG on target.   Not any better.

I haven't tried the 2X, but have been running the 2.5X as it's a very nice optimization of general purpose M4-level magnification sight picture size reticle quality and cost.  At $200 (sometimes less), they were cost effective enough to uniformly buy multiple to standardize on, and I really do like the Quala Of Death .  I sure hope they don't discontinue; but really, there are features and aspects that are legacy. Just like older ACOGs, it's built to fit in the base of a carry handle, and then the mount for Pic rail is what it attaches to, which is a dated configuration today; though no detriments to doing it that way.  

For now, I'm still running the ACOG, for now - but if time allows and I get a few work-projects done this afternoon at home, I may run back up to the range tomorrow morning and do speed / CQB drills with it, to give it that work out. And from that, have a better opinion on the ACOG in such usage.  I still haven't decided what I'm going to do on the 45 degree mount, which was my plan:  4X glass + 45 degree mount; vs my normal baseline of 2.5X for everything (no 45 degree mount).

Neat!
The accuracy with the 55gr is impressive for the RDB..I would have figured it would not like those (accuracy wise) being 1/7.

My 1/9 Rdb (basically a preproduction) also does well with the 50(ish)gr projectiles.

There is another thread kinda like this where a guy (Potts for the Bullpup Forum) tried alot of different ammo and it was reposted on KTOG
..Best ammo with groups under 2" No Targets..
RDB Accuracy Thread

I'd really like to play with one of these. Will probably just grab one eventually. Always wondered if it would fit in my saddlebag but never measured it.

No usefulness gained by this (some lost actually), but I do like the S handguard on the RDB.

Since then, I've replaced the green one with black.

Thanks for the testing & writeup.  I've not had one of these apart, but from the field stripped diagram, is it possible for the rifle to function w/o the top rail & handguard, giving you a free-floated bbl for benchrest precision testing?  That might give insight into future improvements.

Not Really as you cant free float a piston gun as the barrel always attached to the piston in at least 2 places....
You can freefloat the handguard if you wanted to rework where it mounts at the cost of some added weight...I have several piston guns, including an AK with a freefloat handguard and 1 bolt action rifle with a free-floated barrel.

The rdb is capable of moa (or just over) accuracy.. It just takes some looking around for what it likes.


Also..Someone on KTOG attempted to..No affect..best he was able to manage was a free float handgaurd and an F'd up top rail.

Interesting writeup and clever optics mounting.  Sounds like the RDB could do w/ a stiffer chassis.

Im not sure how that would even affect the accuracy in anyway on that rifle.
Desert tech tried stuff like that with the MDRX (and it has an all aluminum upper that everything is bolted into and it didn't really have any affect on accuracy.

Is there something wrong with the accuracy the rifle can produce? What number are you looking for?

Holy crap - I would drink with this guy.  That is some AWESOME work he did, and excellent testing and communication. I'm blown away.  Totally upstaged on everything I'm trying to do here - just awesome thread!   most every idea I had rattling around in my head, he had too - and he broke out a welding machine and tested it.  

I also find his AUG performance data in that thread refreshing as well.  Lots of people keep saying AUG's are 1 MOA capable guns.  Mine's not.  Not even close.  I can shoot 10 targets and cherry pick one that might be close with just the right tuned ammo - maybe.  But his performance is pretty close to my own - in general, the AUG is a 3 MOA gun.  How can it not be, look how many contact points are on that thing - it's ridiculous, combined with short-stroke piston, and tolerances to fit it all.  And a chamber and throat that takes toxic-masculine vulgarity words to describe how oversized they are.  Maybe some people have amazingly tight tolerance machined parts of all the many many contact points on that removable barrel and have found just the right ammo; but his honest AUG accuracy post I believe.  My only frustration is, where are his RDB accuracy posts after all that work?  Why did he just post AUG accuracy performance photos?  Maybe I missed it, I'll go back (there it is, I read too fast) - that thread is GOLD.  Heck, I even tracked the politicians name in his Youtube video to see where this guy even is; because I'd totally buy that guy several beers and pick his brain if he were in Texas! (alas, Washington.  Why so many of the cool people in Washington and Oregon these days?)

But.. wow, after every clever Idea thought I had - that he implemented with a welder and parts -  NOTHING materially improved the RDB's accuracy.   That's a heartbreaker.

Thanks, I was unaware the gas system was similar to FNC's.  So, I tried looking up FNC accuracy, and there's very little on it, other than some claims that "with the right ammo"; it's 2-2.5MOA.  Which is pretty close to the RDB.  Could it really be the gas system that's the source of the accuracy challenges on all this?

hmmm..

OK, here's a question - if you turn the gas all the way off on an RDB, is it fully blocked and "off" or is it still venting up into the gas system, but just not very much?  That's one test to try, - just turn the gas off completely (if you can).

Also, to the HK slap - well that sucks.  I'm also confused, since it looks like it's steel-on-steel parts contacting there, so I would think they could take it... but sounds like maybe not.

AFAIK, the RDB gas system is a bleed-off system.
As in the more open, the more gas is vented to atmosphere vs. pushing the piston.
I think AUGs are, too.

https://www.ar15.com/forums/General/View-of-an-AUG-1-5X-Donut-of-Death/5-2609646/

First - Thanks for that.
Second - well shit, you're right.  That's one of my complaints on the AUG is the gas system vents gas that could be used to push the bullet faster.   I THOUGHT the RDB was a more classic adjustible port to regulate how much it draws.  But, according to KelTec website, they describe it exactly as you say.  Well crap.
https://blog.keltecweapons.com/mastering-the-gas-system-rdb-and-rfb

Though, interestingly enough, my RDB runs with the gas system mostly at full power setting, which I suppose means in my unit at least, relatively less gas is typically vented.  Even hot loads run at just -3 clicks, and my normal loads have to be run at -1 gas, to run reliably.  

Envy.  My CHF CL A3M1 can't do that.  My friends CHF CL A3M1 can't do that.  My other friends malonited A3M1 can't do that.

Sigh.

This may change as you get closer to 500 rounds.

Oh?  Does that erode open with time?

Its got to do with something..Dunno if its that or just the springs settling in.

The RFB is the same way..Except its fewer rounds...

Most Rdbs are right around +5 from open (including mine).

This is ADI 69gr SMK

Oh I've run 69 SMK's, and everything else imaginable.  Maybe the original AUG's could do that; though I have no idea how with that many contact points on the barrel,  but the current A3M1's sure can't do that.

12/31/23 update
cleaning the rifle and relubricate, in prep for a run tomorrow.

remeasured throat erosion after now having fired the 275 rounds.  It's not unusual for the new BBL number to be a bit off, and the "real" number to show up in just a few rounds.  Or at least, with me tha's teh case.

Throat AOL w/ 80 gr remeasured:
2.477"

Mine's 8 clicks from max gas on PMC 223.
5 more clicks to run right with an Omega 300.

1/1/2024 update (will probably break into multiple parts) Part 1 - bench testing again (Part 2 will be the action shooting): 265 rounds fired.

Took the RDB and an M4 to the range today.  I wanted to test the RDB in comparison to a patrol carbine running a 2.5X scope with a free floated FAXON Gunner Match profile barrel.  This is my favorite general purpose M4 16" BBL, as it's very light weight, with standard A2 dimension cut out to going out to gas block, skinny gas block, and then goes skinny barrel to the muzzle, for the weight savings (where the weight savings doesn't hurt you).  Barrel is SS 1/8 twist Wylde chamber cryo-stress treated and malonited.  Pretty much every spec on my "what an M4 barrel should really be" barrel spec list. It's lighter than the RDB barrel, to point to the question - can a skinny barrel of the RDB dimensions (or smaller) actually shoot?

Here is a repeat of the photo showing the two barrel profiles next to each other (note the FAXON goes A2 profile under the handguard, which is thicker than the front).



The RDB is still the same, and while taken apart, I only cleaned the BBL with a boresnake a couple times, and didn't really relube the rest of the gun so much.  Slapped it back together, and off we went.  It still has the ACOG on it.. for now.  We'll talk more on that in the Action section.

Tested several ammo again:
-M193 (my own preferred load of LT32 under Hornady 55 FMJ in random brass, crimped)
-55HPBT, same above exact ammo, but with a HPBT 55 bullet.
-50 gr American Eagle factory ammo.  This is a Federal factory ammo that's quite underpowered (low velocity) for that weight bullet, but historically shoots remarkably accurately.
-M855 green tip (from the Fed Bulk Box buys days)  Factory Hot ammo, GI spec.
-62 SP - barrier blind 62gr softpoint bullets (with a solid copper core in the bottom half, to penetrate windshields and such better).  loaded to a decently warm spec, but clearly not as hot it could be, compared to those M855 velocities.

Short answer: The skinnier FAXON AR15 barrel outshot the RDB barrel, but RDB still shot OK in some groups with the 55 gr ammo, at least some of the time.  But just died with the heavier 62 gr ammo; where the M4 struggled too, but not nearly so bad as the RDB accuracy fell apart.  
Here's the RDB (but I did replace the muzzle device with the exact some one on the FAXON M4 barreled AR, and it has an ACOG on it now).



Exact same dimensions as an A2.  Though it can be a bit flashy in shorter barrels!

Here's the M4.  It's a spare-parts gun, but some degree of thought and hand selectin to it, and is spec'd to be a very light patrol rifle for carrying all day long.  

(I tend to preload my mags and organize sort by color and mag number, hence it's handy having a rainbow of all kinds of the Lancer mags!  Love the clear 20's, handy).
Targets were set at 50, 100, and 200 yards.  



RDB continued to have "a flyer in every string" type of behavior, and really goes to Hell with hot performance ammo like M855 and the 62 gr Barrier Blind ammo.  (where "performance" being a relative term).  The FAXON M4 barrel can definitely shoot well - remarkably well for such a light weight barrel, and the performance and POI doesn't decline as that skinny barrel heats up.  (There are many things I miss from 20 years go - but barrel quality is not one of them!)

But overall, the RDB actually shot ... decent, from the bench with the 50-55 gr ammo.  With the 1/7 twist, it might be possible to find a heavy it likes too, it had some do OK in the prior testing  In theory, i can run some of my national match 80 gr single-load ammo through, which who knows, maybe I'll try it.  

No failures of any kind here, though maybe one mag release button push felt.. odd.  We'll get to that in part 2.
Total round count: 540 rounds fired through this rifle so far.

Does anyone know who makes Kel-Tec barrels?   I assume they don't actually make their own.  (And I may have found part of the problem if they do - barrel fabrication and QC has come a LONG way since KelTec was founded.)

Continuing this update from this day - Part 2 is the action bay shooting.

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Took over a 50 yard bay with side-walls, where you can run and gun and shoot sideways at targets on the sideberms.  Ran up and down the bay with both rifles doing similar course of fire.  Had issues with my timer, so no timed run data to show.  Just some summary items.

Recoil control and Run and Gun:  the RDB recoil is... different.  It's a very mild and pleasant recoil at the bench.  Compared to the AUG which is jumpy and unpleasant, and the M4 is somewhere between.   Afoot though, it was ... different.  My experience is biased by running 4X, which is quite a bit of X for CQB at 5-10 yard running shots.  The RDB recoil is more of a long drawn out push.  It's not a snap recoil with instant snap back into position, but a long dragging slow push, and long dragging slow return.  "long" being a relative term.  But it made doing double snap shots harder, in my opinion, than an M4.  Where a long drawn movement moves the scope off target, and then long drawn closing moves the scope of target, and is harder and more involved to compensate for, to keep the gun on target for the next shot.  Where the AR is snap, and just moves very little, and is back on target when it's done.  Interestingly, the AUG, which I hate at the bench, is an excellent gun afoot, as its recoil while standing is an instant snap, and back on target, and not all unpleasant while standing and your whole body is in play,  It's actually quite good in run and gun.  And so is the M4.  The RDB was.. different.  That said, it did decent.  

In comparison, run and gun with my ultralight patrol spec M4 and the nice LaRue 2 stage trigger, and the good CQB fixed 2.5X Quala of Death Primary Arms scope;  kind of was just better, than the RDB.    I will say, shooting paper at 100 yards, the 4X was certainly better than the 2.5X, especially on finer targets, but the 2.5X still worked fine.

Sighting - Aside: the neighboring group had a guy with an M4 with a 35° offset red dot; which he let me try.  That was going to be my concept for CQB with the RDB while having the 4X ACOG.  TBH, I didn't really enjoy it, didn't find it any faster, and didn't find it helped my target aquisition much.  That said, he ran his in front of the scope (far away), with a tiny RDS (smaller than even typical), and it was partially obstructed by the handles of his scope - so maybe not an ideal run.

Between the above two experiences though, I have decide I'm going to pull the ACOG and mount my spare backup 2.5X CQB instead.  the gun's not accurate enough to realize benefit from more magnification anyway, and it really wasn't a great CQB experience with 4X of power; and my plan of running 45 degree is ... on pause.

Heat:  At first, teh RDB didn't really get that hot, but when I did a couple of 30 round magdumps afoot, that sucker got HOT.  The plastic handguard was not well engineered for hot usage, and even the plastic got quite hot.  I suspect the metal screws that KelTec uses (bleh) to hold it together, were part of the problem.  I was still able to adjust the gas by hand, if I wanted (I found the the hot 62 gr had a good bit more recoil, and so cut back their gas a couple more clicks).  The gun was still usable, but it was definately hot.  

I did a zero-test of heat before/after.  results were odd.  The skinny M4 had zero POI shift at 100 yards, even after cooking it.  But the RDB started at 50 yards already 1.5" low, and when hot, was better zeroed. so it may have moved 1.5" or there could have been some other wierdness where the initial zero test wasn't representational.

Reliability  neither gun jammed.  But the RDB had some wierd and kind of serious issues with the bolt lock.  Where the bolt-lock itself, just LOCKED.  And no amount of strength could depress the release lever.  I had to pull the charging handle, but where the handle engaged the locked bolt at about that spot on the through, it was STIFF and took a good bit of force to force back the bolt that last 1/2" to release the bolt lock part, to then allow going back forward.  I suspect the lock-mechansim is getting stuck somehow, and this hasn't gotten better with time, it's getting worse. I don't know what's up, or if this is a THING with Kel-Tec RDB's, but it's kind of not OK.  Next cycle it'll be totally fine, so it's random; which in some ways is even worse.

Running a couple mag dumps, and the front end of the gun is just SMOKING as various greases and oils are now cooking.  This is typical of running a gun hot, and was expected - and no problem of itself, so much as an indicator that yes, this gun got run hot.  IMHO, every gun needs to be run to this point early on, to find out what's loose or going to break.

And so what got loose on the RDB.    Of all things, the buttstock plate.  those screws came loose and it's wobbling now.  No worries, I'll just tighten that back up.

There were no inadvertent field engaged mag drops.  Though it hates one of my GI mags and won't lock it in.  It loves ETS and Lancer and PMag and GI20's just fine.



Conclusions and plans and to-do:
-Will tighten up buttplate and check some of the other screws.
-Will tear-down and fully clean RDB - maybe remeasure throat (though really that's a 1000 round spread event typically)
-Will take a hard look at WTF is going on with my bolt-lock system.  This isn't OK, and is almost locking up the gun.  not quite, but it takes force to overcome whatever is going on.  And as much as I talk crap about people overfixation on reload speed after they screwed up the first 30 rounds - the reality is, it DOES need to work a lot better than what is going on here.  Hopefully others have some input on this?
-Will swap out a 2.5X CQB (same as what's on the M4) for the ACOG (kind of sad about that - heck, the ACOG is WHY I got the gun; it needed a home!  ah well, maybe it'll go on my field hunting Grendel instead and I'll just take it's 2.5X CQB, and leave my spare still spare in its box.
-My Rhino handrail is to arrive today, so likely will install that too (and of course need all new testing!).  Look forward to suggestions on how best to heat-manage that one, as I bet it gets unpleasant after 3 mag dumps!
-Need to do a repeat of basically everything done today, again with the new fore-grip.  (oh no - my life is so hard).
-If I had to go into extended field duration use in harms way for month, tomorrow, would I take this gun, the M4, or the AUG?  The answer right now, sadly, is the RDB is in 3rd place right now; due to the bolt-release issues, and due to the slower field-double's it feels likes.  Going to work on both of those, and that ranking might actually change, but that's where it is right now.  

Total round count: still at 540.  Only "failures" were very sticky bolt-drops.  That, and it hates my C-Products GI magazine #75.  Donno why it hates #75,but it refuses to lock that and only that magazine in place.  

I have hated the bolt release on the Rdb. Thays why I sprung for the LuckyIrishman enhanced bolt relase.

As far as the hotter 62gr..Eh..double check the top rail and make sure that also didn't work its way loose.Tho..I am kinda hoping it doenst do well with the heavy stuff..More to further disprove the common idea that you need the heavier bullets for better accuracy in 1/7 twist.

Also..sounds like you got one of them keltec qc gremlins,  with the screw/bolts working themselves loose..musta been made in a Friday a closing time 😆

Kel-Tec may do them themselves.  I had one of the Gen 2 SUB-2000s recalled to replace the barrel - the rumor going round at the time was their steel supplier came back a year later and announced they weren't able to continue to certify the previous batch of steel delivered.  It was assumed someone snuck a load of Chinese steel into the market & Kel-Tec got left holding the bag.

I don't mind the bolt release button location or it being a bit stiff.  I'm fine with that.  But it binding up like this is a problem.  I always though the LuckyIrishman version was done for improved placement and a little better tactical feel.  But now I have a doubt that' such is the only reason:   is it also a higher mechanical leverage?  Because apparently this needs a lot more mechanical leverage when mine binds up.

Here are some photos after taking it apart.  The two long tabs, end, where they pup up and will engage the outer parts of the face of the bolt-carrier.  It looks to me like.. is the top one bent a little?  and peened?  Is this normal?  

You are right the recoil impulse on the RDB is different. It’s more like a gentle shove where the M4 and AUG are a punch. After I zeroed my RDB I did some off bench shooting with and was able to shoot fast and accurate with it. Love the rifle but like you said it could do with some improvements.

So the bolt catch is a goofy very long piece of stamped steel, hinged 5" away.  At the bolt catch engagement end, the catch part (circles), rides inside the reciever (top dust cover,/"upper", if you will), via these guide raises that keep it inside (squares), to engage the very outer part of the face of the square bolt carrier (@ arrows).



If something has too much tolerance, it can wedge between the bolt and the upper reciever rail.

Bolt-Stop investigations

Based on some internet searching, my hunch is correct that the thin bolt-stop arms are at times getting wedged between the bolt carrier and the reciever, making it stick pretty bad when the operator tries to release.  

It has been posted by a few: this appears related to hot ammo insufficiently gas-adjusted, and to loose screws; where addressing that will fix it.

I can't confirm that, but I will say I looked closer, and indeed my screws on the reciever were loose, which affects the "track" those bars run in - maybe.  And I was running a wide-spectrum of ammo while Run&Gunning, with not all of it necessarily throttled down to the ideal gas setting, with some of the hotter ammo.

So, I tighened the screws, and I guess we'll see.  I'll tweak the gas next setting as well.  I will say, this gun appears to require more gas adjustement based on ammo type, than any other I've run.  Which isn't a huge deal, but a bit of a regulaion hassle to keep up with.

1/3/2023 updates - no rounds fired, just some configuration items




Installed Lucky Irishman handguard and swapped out the ACOG for a 2.5X CQB. Also cleaned the barrel (some, it's not like this is a 1/2 MOA BBL here).  And moved the ACOG over to the 14.5" 6.5 Grendel, that had been hosting the 2.5X.  That Grendel often has night vision on it anyway.

The Rhino handguard is a substantial upgrade to the feel of the rifle, and more importantly, to the look of the rifle!

A couple items of note though on the LuckyIrishman.  The instalation is more substantial, so no longer able to just pop it off with a simple push-pin.  Alsoit obstructs the removal of the charging handle, and access to the gas system.  

Though, I have not been cleaning the gas system and am  not sure i I even am supposed to.  The owners manual is pretty vague when it comes to cleaning the gas system, so it's unclear if I should pull the plug out and clean all of that on a regular basis, if ever.

You may want to loctite those fasteners with something high temp, not just tighten them.

MDRx trunnion fastener flashbacks come to mind.

That's the Raptor handgaurd.


There's a thread on Ktog (i can find it if you want) about cleaning your gas pistons.. I dont recommend doing that alot.

I fairly sure,while a little harder to access (vs using the Keltec Handgarud), you can pull the piston out and clean it and reinsert with 2 fingers..

If you don't want to keep the LI handguard on to access you gas piston...you can simply undo the front handgaurd screws and pull the whole thing off. This is also what you need to do to swap the sides of the charging handles..dunno why you would do that.

I have not needed to do that since I got my handguard.



There's no heat concern in the polymer "lower" that runs from to the rear of the triggergaurd to the buttstock..
Blue loctite is fine..

If the rail screws by the gas block are loose, those will need something high temp (don't screw in all the way the rear top rail.That needs to float a bit.Screwed all the way in,that rear bolt will stop you from charging the gun.

Here is the RDB next to an SBR'd 10.5.   Note which one is shorter.  

Uh...
The 10.5 SBR?

Update 1/7/2023. Will post the details in additional separate follow up

Overall rifle is working well.

Main item of note is the bolt sticking on lockback.  Tightening screws and softening recoil with ammo and and gas settings has done little (nor did I expect it to).  I suspect the arms are serving and sticking between the bolt carrier and receiver walls.  

I have to rack the gun manually with some vigor, to charge the next mag, as the button is far too stuck to work most times.

How do others address this issue?