Wanted an RDB, then an RDB-C, then an RDB-S, and finally bought an RDB defender

I've never had a bullpup or a piston gun, so this a whole new deal to me

So far I am totally digging it. I wanted to throw a TR-24 on a survival for a lightweight gun that could reach out a bit and take advantage of the 16" barrel. Since I ended up with a more tactical model I tried it with a TA-33 and did not really love it. I had to mount the TA-33 all the way back on the rail. The rear section of the rail is cantilevered and the flex caused a lot of issues

I ended up throwing a HS510C on it, and making it more of a SBR replacement, which was not my original intent, but it works really well

• 9.2 lbs - FREAKING heavy! Mine was 6lbs 12oz in stock config, and with everything show it is 9lbs 3oz.


• 30.75" Oal - With a suppressor, and 16" barrel, and a stupid long LOP


• Toolless adjustable gas piston - basically what everyone is begging for on an AR, and I don't know enough about pistons to know if it is long stroke, but the action can travel almost a full inch past bolt lock back, which is pretty sweet. It is also quieter than a 16" AR suppressed


• MLOK Rail - The only reason I went with the defender model, it's loose - think sloppy A2 handguard fit, but I just use it for a light and grip. Foreend pressure definitely affects POI though, so for accuracy think airgun style


• Top rail - The rail is a weak point in the design, it is super beefy, and still can have some flex, especially over the cantilevered part. I would prefer it lighter and smaller, or the option for a lighter and smaller one


• Ergos - Very good, I love AR ergos, and this doesn't best an AR for me, at least not yet, but it is pretty easy to play with, and I think I will grow into it more as time goes on


• Bottom Eject - Coolest thing ever, I need a bag for it


• Ambi - check


• Barrel - 16" Melonited 1:7. I'm getting about 2MOA prone with a bag at 50 yards with my bulk 55gr reloads, My larue barrel with the same bullet (and a scope) will do sub MOA

So far I only have about 300 - 400 rounds through it. I have cleaned and oiled it, and barely messed with the gas. I have had no issues yet. It really seems to be suiting the HD role. The 510C mounted pretty far forward on the rail also seems to be the perfect optic for this role, I can't seem to bring the gun up without the reticle being immediately visible, and easy to drop onto a target, it's just fast. Speak of fast.. 16" velocity in a 10.5" sized package, it's easy to handle, easy to swap from L to R, and has good ergos for reloads, light activation etc. I still need to come up with a sling solution for it, and it's pretty weak on KT's part to put some HK loops instead of QD cups on it. Besides the sling, my only future plans are to reprint my 3d furniture in PETG Carbon, and perhaps sand down the waffle texture grip and stipple it, and shoot the crap out of it. If you guys are (un)lucky I might even make one of my stupid youtube videos of it

Looks good.

I love my RDB. Would love it more if I had that rail. May have to pick one up.

Kind of disappointing to hear that the rail has so much slop in it.

Handguard or top rail?

The handguard doesn't seem to be an issue to me, everything I want to put on there is still solid, and the little bit of slop seems necessary for the design, actually makes it a bit more "free floated" than if it were rock solid

The top rail is weak, especially for how bulky it is. With the long LOP optics need to go farther back, and I chased the POI around on the TA33 trying to get a super precise zero. I was also about to drastically change POI at a few hundred yards by placing my support hand over the fiber to darken the reticle

Is that something the aftermarket may be able to address?

The aftermarket is a lot smarter than I am, but so is kel tec. Without some major redesign I don't think this thing will ever be a tac driver, I honestly think it's best suited to a red dot gun type role.

You could absolutely stiffen up the design, but it likely wouldn't be worth the expense to Kel Tec.

New lower receiver group that extends past the barrel trunnion area, providing a sturdy place to hang a foregrip/rail off the front of, and a sight rail on top of.  Basically a long U or H shaped aluminum channel profile that the foregrip, barrel trunnion, FCG, grip, magwell, and top cover pin onto.  At that point the current optic rail would just be a cocking handle support & could thin down.  Would be a radical re imagining of the whole concept.  Check out the Madsen LAR prototypes for a similar sort of architecture.

The fundamental issue with trying to add a free float tube to the existing design, is the receiver isn't tubular, but a clamshell, connected by the barrel trunnion itself.  It's not intrinsically tight or rigid, and it's definitely not easy to attach a full-ring tubular member to the front of it.

Curious as to whether you are getting any gas blow out towards your support hand on the side opposite the charging handle.

So basically if I shoot lefty? I'll try

Interesting question.  The long stroke piston operation, and downward ejection, seem to make this an ideal suppressor host. No direct route to the eyes/mouth for the gas.  I hadn’t thought about where the piston vents.  I’m also interested to know.

It's tappet, not long stroke, venting is out the front (sort of, the vent kinda points at the barrel)