M*CARBO Brotherhood

AR-15 Buttstock Adapter For Your SUB-2000?

The question was asked "What about creating something that would allow you to use an AR-15 Buttstock on your SUB-2000?"

I agree completely! I wish it was already setup that way. Would have been a much easier option to incorporate that feature into the gun design from the beginning.

The problem is since the bolt tube/receiver is the only serialized part on the SUB-2000 that piece is technically the firearm. We have to leave that piece in place. There is your first design constraint.

So now we have to think about how do we add something to what is already there to make it functional with all AR-15 Buttstocks? We have to look at the AR-15 Buffer Tube and add those features to the SUB-2000 Bolt Tube.

Second design constraint is that the SUB-2000 still needs to fold.
On the SUB-2000 Buttstock there is a cut out to all the front sight to drop into.

Third design constraint is that the barrel and receiver needs to lock into place when folded in half.

What are you thoughts and ideas so far? You don’t need to provide a finished solution just start throwing out some ideas here.


Folding would definitely be an issue. I’m not sure what the size difference is between the Kel Tec sub tube and the ar15 buffer tube.

But if possible you could make a sleeve to cover the tube on the sub that fits the ar15 stocks. Providing the sub tube isn’t to big.

As far as latching the gun I would think an adapter could be made to lock it to the new stock somehow.

Of course I’m just guessing I don’t know anything for sure. I don’t have an ar15 stock to compare to my sub, lol. But I’m working on it, my first ar15 receiver is in the mail.


The real problem is that your Kel Tec Sub-2000 's Serial Number is located on the buffer tube. The modification would have to allow the serialized portion of the rifle remain on the rifle.


I was thinking an adapter could possibly slide over the tube on the Kel Tec . That way the serial number would remain. I mean it could be covered up as long as it’s there right ?


Yes as long as the part is still on the firearm it’s all good. I think some sort of adapter that will bolt on the end would be a good start. Thoughts?


Another consideration is the very low height of the sights, especially the rear sight. People already very commonly complain about not being able to get their head down low enough on the recoil tube to get a good sight picture. Anything added to the recoil tube, slid over it, etc will only make that worse by increasing tube diameter. I’ve even read where people installed a rubber tube cover and took it right off because even that little bit made a big enough difference to them. Sure, you can make taller and taller rear sights…until you run out of front sight elevation adjustment… Yet another design constraint.


Actually, they put the serial number there for a reason. To make it very easy for people to replace receiver halves to change colors or whatever. No FFL involvement anymore as before because, previously, one of the receiver halves (left?) was the serialized part, aka the actual “firearm”. And, it’s also not an “insignificant” part. It’s the very core of the rifle to which everything else attaches. If anything, it makes more sense to serialize the tube instead of one of the plastic receiver halves.


And, would the serial number have to remain visible, too? Not sure if that’s an actual requirement, though.


I meant easy to duplicate (INSIGNIFICANT)
I have several handguns serial # is under the grips


Take yours apart sometime and/or watch a disassembly video. That tube is not “insignificant” to make, nor is it “easy” to duplicate. There are some quite complex machined cuts on it inside the receiver, especially where it dovetails/locks into the receiver halves. It goes all the way up to the fold hinge and also incorporates the mounting lug for the feed ramp. It’s not just a straight tube with some simple cuts.


it didn’t seemt o be the heart of the weapon imho.apparently I have not paid close enough attention to that detail I only received it yesterday …ghave not even fired it yet have to wait for the snow to stopfalling long enough forgive my obvious ignorance.


No problemo. I actually thought the exact same thing at first. “Man, I could just cut one of these tubes myself in my garage!” Then I took it apart to install M*CARBO internals. Nope. LOL

Also, Kel-Tec had to get approval from the BATFE to move the serial number and they wouldn’t have approved it if the part were easily duplicated. I actually asked them about that very thing back when I thought it would be “easy”.


We’re definitely going to put together a crude prototype to at least communicate the idea properly. Pictures always explain this sort thing much faster.

Should have something in the next day or so.

Don’t expect anything finished or complete.

Just a crude prototype to see if the idea is even worth pursuing.

Looking forward to your feedback on this one.


what about modifying aan ar pistol brace…like others are saying, something to slide over t bolt tube but modify the butt end to receive the site when folded


I REALLY like that approach! Plus, for our elder / disabled shooters, it would help provide better (and safer!) control of the firearm. GREAT idea!


What if we also explored the idea of some sort of blade/fin that covered the existing butt stock or attached. These are catching on like wildfire in USPSA.


I made an ar buttstock adapter for my gen1.
I went back to stock but it worked fine.
Used a spare buffer tube and sanded the inside diameter so it will friction fit over the bare sub2k tube. I also hacked off the closed end so it was an open pipe so the action can still be removed. I needed to mill and grind for bolt handle clearance. Ill dig it out of my parts and add pics later.


I think it would be a tricky thing to make the tube into an ar style buffer tube to accept various butt stocks. I think it may be more feasible to just pick a certain ar style butt stock and adapt it to fit the stock tube as it is. It may not have the quick adjustability of an ar stock, but would have the better ergonomics of an ar style stock.


That’s actually a pretty good idea!


Can you still attach it? Interested to see.