questions on swapping a2 stock for ubr...

[broylz]

I have the hunting model with the bull barrel and the magpul a2 style stock... I am getting a ubr for it but am unsure what differences I will need to make. I pulled the buffer and spring and it seems to be a carbine setup with a plastic spacer. When I tried to remove the stock, the buffer tube came with it as I think the screw is held in place with some lock tite probably.

Is it going to be a matter of ditching the a2 stock and buffer tube and just running my buffer and spring in the ubr tube or will I need to have a shorter spacer or anything else I'm not aware of?

 

[broylz]

Ok so I went for it and just measured the buffer tubes side by side and it seems like the ubr tube was just right about the same length shorter as the included spacer was so I threw it together. Turns out the buffer and bcg combo was much too long and the buffer was hanging up in the stock as well.

I swapped out the factory parts for a buffer and spring kit from heavybuffers.com that is supposedly made for the 308 with a normal ar15 carbine buffer installed.

Good news is the buffer doesn't hang up anymore but the bad news is it is still too long. It is short enough that I may get the rifle to run occasionally but too long where the bolt catch will not work as the bolt does not move rearward far enough...

So now I'm at a loss... I've read a few threads over the net saying others have used a ubr with the heavy buffer kit but mine is not working and I'm not sure why. I have sent heavybuffers.com an email asking if they have anything shorter and I have not received a response back on it yet, only that I should have the proper buffer and spring.

I'm really debating calling s&w to get a carbine tube from them and running the ctr I have for now until I can sell off the ubr and go from there again .

 

[bergermeister]

For what it's worth.. (your thread isn't getting other responses)

I personally like the ol'e military-style A2 buttstock, and not familiar (by personal choice) with the Magpul. I have found that the A2 buffer tube is almost exactly 2" LONGER than the one that came on the collapsible contraption that came on the MP-10. Meaning; a 2" plug dropped into the A2 buffer tube would bring the factory recoil spring/buffer into S&W spec's. The plug (depending on material) could add weight to the butt..or not. An MP-10 fitted with the A2 buttstock lash-up should run the same way the rifle left the S&W plant without the tinkering.
Probably though, you are not mil-spec A2 kind of guy?

 

[MistWolf]

While the spacer does allow the installation of the A2 stock with the rifle length RE, I would like to see someone come out with a longer buffer to allow the the use of a longer spring. This would have the same affect as installing an A5 RE on a 5.56 AR, which allows the use of a rifle length action spring, improving felt recoil.

In the case of the UBR stock, I suspect that a little trimming of the nylon bumper would get it working for you.

However, if you are to switch stocks, let me suggest using either the standard S&W carbine style RE or the VLTOR 6 position A5 RE and a Magpul Fixed Carbine stock. It's much lighter than the A1, A2 or UBR stock and gives you a cheek weld along the entire length of the RE. It also allows the use of the thicker PRS recoil pad. (I think Limbsaver also makes a PRS recoil pad)

 

[broylz]

Had debated trimming the bumper on the buffer but I would almost need it flush with the metal to work reliably in my mind. Also thinking about trying an ar15 h3 buffer as its a tenth of an inch shorter and then I could trim the bumper if need be as well.

That said, I haven't gotten a response from heavybuffers.com since sending in pics on Monday so I will try to call him on tuesday. I'm thinking of just getting a standard carbine RE from s&w and running the factory carbine setup with my buffer and spring and a ctr I have in my parts box. Selling off the ubr gets me really close to a mi ss m lok handguard and I may be trimming my barrel to 14.5 like another member here, sorry can't remember the screen name off hand.

 

[MistWolf]

What is the length of that Heavy Buffer compared to a carbine buffer?