I started a run on this… I never placed my order and now will be recovering from a surgery for the next 6-8 weeks… can’t wait to hear if this works as advertised. I was hoping it would fix my trigger from following the bolt home a few times a magazine.  I have the spikes 9mm buffer and a ramped colt bolt but still have trigger issues, years ago m-60 joe fixed one of my pre ban lowers and told me about ramping the bolt and to shim the buffer to stop the bolt catch form breaking off. I have a HK94 that I can not bring myself to SBR. I really like sticking with the same manual of arms so the ar 9 it is. For now…

Ship notification received here as well.

This is what I know this morning. In order for the RDS to function, the BCG weight must be removed to allow the bcg to travel over the “guide rod” into the buffer tube.  In my short test, this turns my AR9 to not a single shot SBR. The bolt strips a new round but doesn’t reset the hammer.
I have a few thoughts but ran out of testing time. 1) the light weight of the bcg travels back and forth faster than the hammer/disco reset. 2) the bcg doesn’t travel rearward enough to reset the hammer. I’ve sent an email with pics to Maxim and await their reply.
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Bummer to hear you're having trigger reset issues. Any chance your receiver extension is shorter than a standard carbine RE (which is what their standard buffer is designed to operate in, if I'm reading their site correctly) and not allowing your bolt to come back far enough?

Can you dry fire, hold the trigger back, and reset the disco by cycling the bolt? Seems that would rule out the "not enough room to travel back" theory and maybe point towards the rollers providing too much resistance for your load?

What ammo/load did you use in it? I presume this has given you no issues with your standard BB bolt weight/buffer combo.

Is your bolt ramped? What trigger are you using, looks like a Geissele trigger, did not know they made a pcc trigger. The buffer in my cqb stock has a way shorter rubber piece. Attached File

I would swap triggers and try again.

Shipping notification from Maxim yesterday, carbine unit on its' way!

I have to admit I'm a little stumped on how the locking piece unlocks the rollers when you pull back on the charging handle.

In an MP5, the charging handle pushes on the BCG, which PULLS the locking piece backward, unlocking the rollers in the bolt.

In an AR, the charging handle pushes on the BOLT, which pushes on the front (locked) piece, not the locking/unlocking collar.  The rear collar, hiding behind the front locked piece, needs to move backward for the bearings to come out of the notch in the guide rod.  How the heck do the bearings move outward enough to unlock when hand cycling using the charging handle?

What am I missing?

It's not truly locked, but you have to overcome that mechanical advantage to charge it.

@str8shuutr45
How much more difficult is charging?

I don't have one and have only seen some pics, so I may be totally off base.

I suspect it's the same way an MP5 works when fired: case pushes bolt head which via the rollers and LP pushes the carrier back. If this is the case, pulling the CH would be pulling against the leverage of the delay.

Guessing, the CH actuates the carrier which tries to move the front piece with the bearings in it which are also seated in the recess in the recoil spring guide. In order for the bearings to move out of that recess, they force the larger weight rearward. So, the MP5 trunnion recesses analogous the recoil spring guide recess, the MP5 LP angles to the conical angled surface of the large rear weight, the MP5 carrier to the large rear weight, and the MP5 rollers to the bearings.

Got it.  I have to admit I didn't believe you, so I stuck a cleaning rod down the barrel of my MP5 and pushed on the front of the bolt to see if the bolt would unlock without moving the locking piece out of the way.  It took a fair amount of force, but sure enough it did unlock and move backwards.  Thanks!

Now that I think about it more, duh, of course it will.  Jeez I need some coffee.

This would be a great comparison wouldn't it?  How much force to unlock compared to an MP5.  Hmmmmmm.....

That's why the MP5 bolt assembly can be ~12oz while the sweet spot for straight blowback 9's is 22+oz.

Which means... (oh god, here he goes again!)...  the locking collar's internal surface must have an inclined cut angled outward toward the front or the collar, like a funnel, or it would not move backward.

Obviously, delayed blowback is not my forte...

That's my presumption. And while I'm guessing, I also suspect the taper on the recoil spring guide, only seen on the shorter version, is analogous to the roller marks that can sometimes occur on a MP5 type receiver when the BCG impacts the buffer too hard, giving the bearings a place to go without damaging anything at the end of travel while also gradually guiding the pieces back into place with the tapers.

Ok, I was able to test the gun out for the first time with about 350 rounds (tested 115, 128, 147 FMJ - Cheap target ammo)  with the CQB model and the maxim CQB tube. I ran this all suppressed, suppressor is mated for life with this gun since its tucked under my rail.

I did have to remove the pinned weight from my KVP BCG so that it would allow room for the guide rod of the RDB system to go through it when the bolt moved back

Absolutely no issues at all and the recoil was significantly improved over my previous setup.  (I used the JP SCS setup with a short buffer tube previously and before that I had a Flatwire Standard Spring with KVP 10oz Extended Buffer with a carbine tube). Gun was working flawlessly before as well btw.

I ran this gun with just a plain buffer tube (no stock/brace) so the recoil difference was extremely noticeable for me with this new RDB system. Instead of getting punched around, it was more of a nudge and I was able to get my dot back on target very quick.


Only drawback is charging the damn thing. It takes a bit more force to charge it but I found If I just do it in a quick motion, it is not too bad. Maybe the carbine version would be easier to charge.



My set-up:

Maxim RDS CQB Version + CQB Buffer Tube
KVP BCG (pinned weight removed)
Macon Barrel 4.7"
CMC PCC Trigger
Aero EPC Upper + Lower (LRBHO works)
Suppressor - Banish 45
Glock 19 Mag/Magpul Mag
Radian Safety
Radian Charging Handle

Wonder if you could run a short version of the Maxim w/ a hydraulic buffer?

Any noticable difference in port pop and/or gas?

Would have to be annular, since the rod should be stationary

Behind the Maxim, not in front.  

Might need a rifle-length tube.

I wouldn't say its a significant difference but it does help. Running the suppressor in the shorter configuration versus extended helped more though, as I was still getting some gas to the face.

If you did that, the locking effect would be partially negated by the compliance of the buffer letting the rod travel reward.

Maybe a really stiff hydraulic piston that only compresses when the bolt bottoms out?

It would be simpler to make new large rear weights that are heavier and/or change the angle of the conical surface at the front so it doesn't bottom out at all. Perhaps they will offer them in the future from the manufacturer.

Mine just showed up, and without reading the instructions I went right to my girlfriend's backup PCC that is Scheel equipped to install it.  Ran into a snag immediately.



Once it got to this point it was stuck.  I mean properly stuck.  It was wedged between the buffer tube and the hammer.  I had to unscrew the buffer tube to install it, which for all I know is part of the normal installation instructions.  I am sure that the CMMG hammer complicated this.  I have an SBR that also runs a Scheel, but it has a Hiperfire trigger and it may not need to be disassembled for installation.

First impressions are that this thing takes a lot more force on the charging handle to unlock than the Scheel ever had with any spring combination.  This is promising.

Will this be better served w/ a side charger?

My girlfriend's gun has a Foxtrot Mike side charging upper on it and I do think that it helps to charge it.

I was kind of wondering this myself from a wear and tear standpoint.

I just put it in my other Scheel equipped rifle that has the Hiperfire and it dropped right in without removing the buffer tube.

What instructions? There was nothing in the box I received today except the buffer assembly in bubble wrap. I have a standard mil-spec trigger and I too could not get the roller end past the trigger. So off came the buffer tube, insert buffer assembly, and re-install buffer tube. At least it gave me the opportunity to remove the buffer retainer thingy. Yes, difficult to charge, especially the initial pull back - don't think I would want to use this with endo mags where you have to lock back and then remove the mag.

For funsies I stuck a cleaning rod down the barrel of my MP5 and used a scale to measure how much force it took to unlock the bolt.  It averaged about 12lbs, with a 9.6oz bolt assembly.  I'll run the same test with the Maxim when I get it, but with most 9mm AR bolts averaging 12oz. (without the rear weight). It's starting to sound like it may be oversprung, at least the PDW version.  I wonder if they'll offer additional spring weights.

For anyone who has one of these and has shot a gun with it installed, what ammo have you been using?

I fired a couple in my back yard to check function earlier, which extracted and chambered the next round just fine.  They were an RMR heavy plated round nose 147gr over 3.7gr of N320.

We currently have a torrential downpour, so I may not make it to the range for a few days to really test it.

Sorry, I’ve taken so long to respond.  I was taking a two day Precision Scoped Rifle course.  
The receiver extension came with the Maxim CQB stock.  I honestly got frustrated and decided to just take the RDB out.  This gun has run like a sewing machine sine I first built it in 2008.  I’ve changed the upper to side charging and have swapped the current Geissele super three gun out a number of times (binary, LaRue, FRT) without a problem.  The can is an old Liberty Suppressor’s discontinued design called the Fat Cat. I only shoot 147 gr plated RN over 3.7 grains Titegroup. I have another “backpack version of an AR9 that I will play around with.  I’ll try another trigger to see what happens.  Unfortunately, it’s on hold for now because we are going out of town for a few weeks.  I’ll keep a close eye on this evolving thread.  Thanks guys for your support.

Maxim Carbine Roller Delayed Blowback buffer system first impressions (no live fire yet - will need to wait until at least Monday).

I just received the Maxim Carbine Roller Delayed Blowback buffer system and run some tests in the workshop.

I decided to test the unlocking force of the Maxim compared to an MP5 by sticking a cleaning rod down the barrel and pushing on the bolt.  This should give the amount of unlocking force needed to overcome the mechanical advantage of the rollers.

My MP5 required an average of about 12lbs. of force on the bolt face for it to unlock and start moving backwards.  Now I was pushing downwards with gravity, so we need to add the 9.6oz. bolt to the pressure, so around 12.5 lbs.

The Maxim system required around 14lbs. of force to unlock the bolt and start it moving backwards.  Add the 12oz hollow bolt and we have about 14.75 lbs.  

Not too different, but there's a catch.  The charging handle of the AR was never designed to give the user much leverage.  For more leverage, you often need to mortar the gun, like when unsticking a stuck cartridge.

The MP5 charging handle is designed so the user has the leverage of their whole arm and can press the handle with the palm.  The AR charging handle only allows 2 fingers.  It's MUCH harder to pull the AR charging handle back wth this much force holding the bolt in place.  I needed to hold the forearm with my left hand and pull FORCEFULLY back on the charging handle with my right to overcome the Maxim system and charge the gun.  Not optimal at all.  It may work better with a side-charger or with a larger handle.

I also got the Anarchy Outdoors adapter to see I could make a Law Tactical folder work with the Maxim system. First impressions are NO.  With a regular buffer tube setup the bolt just barely touches the Maxim system.  When I use the Anarchy adapter and close the buffer tube, it pre-loads the Maxim RDB by a millimeter or two, essentially overriding the roller delay's mechanical advantage.   It may be able to be modified by shaving it down a bit on the end, or unscrewing the buffer tube a thread to minimize/eliminate the contact between the adapter and the Maxim buffer when closing the tube, but for now, it's not looking good.

That's all I've got so far.  More to come.

As you alluded to elsewhere the MP5 charging handle acts on the carrier, so the user only pulls against the recoil spring and NOT the mechanical disadvantage of the delay. The Maxim acts on the bolt, so the user pulls against the mechanical disadvantage and the recoil spring. In order to avoid that, the CH would have to act upon the large rear weight which is well within the buffer tube. So, while a side charge or larger handle would be better, it will never be as easy as a MP5.

After reading some of the comments here, my RDS is going to be used in a carbine with a left side charger NFA upper. I don't use many rear chargers anymore, anyway.

Thank you for doing that
Do you know how much force it takes to fully compress a regular blow back bcg and carbine spring? I'm trying to gauge how difficult it will be

Sounds like it could really use a notched buffer tube and rear charging handle underneath a la SUB-2000.

The more I read these comments, the more I think this thing is more trouble than its worth. I will keep following though to see what happens.

Sounds like exactly what I need for a silencer host.

Yes, that's what I thought based on the design.  Later I put the scale on the handle and pulled it back and it was practically the same, so I don't know what's going on.  I'll investigate this further when I have the chance.

A normal carbine spring applies about 6lbs of force at bolt closed position, so this is what you need to overcome to start it moving.  Full compression is about 12lbs when it stops at the rear.

Yeah...it's a bummer.  I'm still looking forward to testing mine but think with this design, I may want to get a steel charging handle.  Sometimes you run into ammo related malfunctions where you have to mortar the round.  Having to mortar the round plus fight this mechanism would suck.  

I got my 8" suppressed SBR up to the range this afternoon to test this Maxim RDB out. Myself, my girlfriend and a fellow USPSA shooter ran it in several configurations.

The plusses:  on my 8" upper with suppressor, it was very quiet. Port pop was nearly eliminated compared to a straight blowback system with an extra long 8oz buffer and Tubb 308 carbine spring. With my girlfriend's 16" Foxtrot Mike side charging upper it was relatively easy to charge, and the gun had very little bounce.  Neither upper experienced any malfunctions of any sort.  No short stroking, no failures to go into battery, no out of battery firing (I had a 16" AR9 blow up last week from an out of battery) and I think this buffer will dramatically reduce the incidents of this happening.  With my girlfriend's upper the side charging handle made it significantly easier to charge, but she still struggled on an uncocked hammer.

The minuses: with my Hiperfire 3G trigger and the heaviest springs, with an uncocked hammer it took a tremendous amount of force to charge the rifle.   My girlfriend physically could not pull the rear charging handle back on my suppressed upper, even with an extended latch. The gentleman who was with us is fairly small and he also struggled to charge it.

My take:  this thing is very effective at reducing recoil, and keeps the bolt closed long enough to prevent port pop on a suppressed short barreled upper.   The 16" barrel with a Miculek style brake on it was very soft shooting without a lot of bounce. Fast double taps are very easy.  I think Hiperfire triggers are a no go unless you are pretty stout (I am a 6'3" 260lb gorilla) due to the extra charging force.  When the buffer was briefly in my girlfriend lower receiver with the CMMG trigger it was significantly easier to charge.

I decided to burn even more money and bought a TACCOM Super Feed 16  ULW-B (mid brake) barrel, a Joe Bob Spartan side charging upper, a TACCOM bolt and a 6oz full carbon fiber handguard to build a new competition upper to test with this buffer.  Parts should be here this week, and I have a match coming on Sunday so I will give my thoughts after that.

Range report - Maxim Defense RDB buffer system -

Used my Franken pistol (not suppressed) with 5.25 inch barrel, FM 9mm lower with LRBHO, Faxon bolt with weight removed, and standard mil-spec trigger. Shot 120 rounds or so of mixed 115gr ball, a couple different brands of 115gr JHP, and 147gr flat nose - all fed, fired, and ejected correctly. Did not lock back on first 2 empty mags, but then did on subsequent mags so I don't think it had anything to do with the Maxim RDB.

Yes, soft recoil. I would would say a little better than the CMMG RDB (I have a CMMG RDB 8" pistol). The only downside was the significant difficulty in charging.

Rear charger or side charger?

FYI, I use Geissele SSAs in both of the lowers that wear 9mm blowback uppers with ramped bolts without issue. I've also run the upper with a ramped Colt-style bolt on my RR M16 with a G SSF and it did fine in semi and full auto.

So...I too have run Geissele SSF's in full auto in various configurations including straight blowback 9mm...but I always test with a standard M16 fire control first and make sure it is tuned so that there will be no trigger slap.
I think it is fine IF you make sure your configuration isn't beating itself up and not everyone is going to make sure their configuration is safe for said trigger so Geissele doesn't support it.
Geissele will void the warranty of running the SSF in pistol caliber as stated on their site:
https://geissele.com/super-select-fire-sopmod-ssfr-trigger.html
"Please note, our triggers are designed for mil-spec AR15/M4 carbine rifles. Our AR15 triggers are not compatible with the Sig MPX/MCX weapons or Pistol Caliber Carbine AR15/M4 variants.  Using them in these platforms will void the warranty."

BTW, they state the same thing for the SSA: https://geissele.com/super-semi-automatic-ssar-trigger.html

As for charging force, Maxim needs to come up with a levered charging handle ala HK G3, to essentially break the lock with mechanical advantage and then charge with normal effort.
Or have a floating link so that the charging handle engages the locking ring directly for a short distance before engaging the carrier.

Would be nice but I don't see how that is possible without a redesign and at this price point.

I just got mine today and looks well machined.  Looking forward to some testing.
I don't see any instructions with mine either.  Unless you want to call the label on the box instructions.  It is just descriptions on the label.