armalite 308 compatibility.

[sheepdog697]

can i swap out a rifle length buffer tube on an armalite ar10b, with an ordinary adjustable buffer tube and stock? Or will i have to buy a proprietary armalite 308 buffer tube and stock?

thanks in advance

 

[flyer]

What buffer do you want to use?

 

[sheepdog697]

i currently have the rifle length buffer with a standard A2 stock. Just trying to figure out if i need to go with something like the UBR from magpul to use the existing buffer or if i can simply swap out for a milspec carbine buffer and use any of the stocks associated with those.

Thanks

 

[flyer]

I think the UBR uses an "entry length" buffer tube which would require a DPMS style shorty buffer and matching spring or maybe a JP SCS (I think it's compatible).

If you want to use a standard AR15 carbine buffer in it you need an Armalite length tube which is 3/4" longer than an AR15 carbine or "entry length" buffer tube. This is also the same length as the Vltor A5 buffer tube (but in a large frame AR an A5 buffer is too long), POF uses the same length for their P308 carbine and for the budget choice, PSA uses that length for their PA10 carbine (recently at least) but it's a plain Jane tube not as nice as the others.

I've bought POF's P308 buffer tube kit that includes a standard buffer and spring, it's nice and won't cause a mismatch. Depending on your gas system you might want a heavier buffer or adjustable gas to tune it.

 

[PlinkIt]

The ubr also has the A5 length set up, and by my memory was only about 0.010"-0.020" off from the armalite carbine buffer tube

The springs for the rifle length and carbine length armalite set up are the same, you only need the different buffer (just order it from armalite / call them, explain what you need, they are nice folks and will make sure you get the right thing)

I have spoken with armalite myself about using a UBR on the B pattern rifle, and they wouldn't verify it works... As they hadn't done it, but they don't see any reason the ubr won't work given the measurements I was getting.

I can take measurements later to show the difference between the items if you can wait a little

 

[Strykervet]

I'd call Magpul, they can tell you straight up.

I just put a UBR gen.2 on a Grendel and I had to get the A5 VLTOR buffer and spring, which is nice. But when the UBR came, it also came with a little plastic plug that fits in the end of the buffer tube and allows use of a regular AR carbine buffer and spring. I'm not sure if you can use that kind of buffer in a .308 Armalite though.

It's a really nice stock, I was surprised, lots of adjustment locations and it's not nearly as heavy as I thought it would be. Not like the PRS, that thing weighed a ton.

 

[flyer]

Ok, with the spacer that sounds like the UBR has an Armalite/A5 length buffer tube which should work on an AR10 with an AR15 buffer and AR10 Carbine spring.

I didn't know Magpul was so forward thinking because the UBR has been around for quite some time.

 

[PlinkIt]

Ok, with the spacer that sounds like the UBR has an Armalite/A5 length buffer tube which should work on an AR10 with an AR15 buffer and AR10 Carbine spring.

I didn't know Magpul was so forward thinking because the UBR has been around for quite some time.

Just to make sure we are on the same page...

There is NO difference in the carbine or rifle SPRING in an AR10...

WITHOUT the spacer in place you have a A5 length buffer tube in the UBR

WITH the spacer you have a standard AR15 length carbine buffer tube

You DO NOT want to use a standard ar15 buffer in the 308 you NEED a heavy buffer.

 

[flyer]

Not necessarily, the POF P308 uses a standard weight AR15 buffer. It really depends on your gas system.

Some people tune for a standard buffer and a light weight BCG, some tune for a full weight BCG and a rifle buffer or H3 buffer so standard weight BCG and standard buffer is around the middle of that range.

I'm not saying a heavy buffer is a bad idea but if you have a standard AR15 buffer you can try it before you go out and buy a $$ heavy buffer.

 

[PlinkIt]

@flyer I'm with you, if he was working on a pof or jp .... Or anything that might have a lighter BCG

But I've never seen an Armalite that didn't have a heavy ass bcg in it from the factory, and we are supposed to be giving him information on his Armalite.... Trying not to send the guy down the wrong road since he told us what he was starting with

 

[Mike_in_FL]

In an Armalite B model lower I used an original UBR with a Tubbs flat spring and a Slash AR10 CAR buffer. I was also running a JP AGB on the upper so I had no problems at all. As everybody else has stated, the UBR 2.0 uses the VLtor A5 buffer tube.

 

[PlinkIt]

Measurements I promised

Understand when I reference AR10 I am speaking of ARMALITE

Here are some rough dimensions on the buffer tubes
AR15 carbine buffer tube 7.05"
AR10 carbine buffer tube 7.72"
UBR buffer tube 7.75"
UBR spacer 0.7"
RIFLE buffer tube 9.7"

The AR15 &AR10 carbine buffers are identical size but you will notice the AR10 carbine buffer from the armalite is a H3

The rifle length AR15 buffer is nearly 3/4" longer than the AR10 buffer

Left to Right
AR15 carbine buffer
AR10 carbine buffer
AR15 rifle buffer
AR10 rifle buffer

So to recap

Changing an AR10 rifle length system to a AR10 carbine system should include an AR10 carbine buffer tube (or A5 length system will be less than a 1/32" longer)

Then you will add a HEAVY carbine buffer to match original Armalite set up

Use the same spring that was used with the AR10 rifle buffer, as Armalite uses the same spring for both

 

[sheepdog697]

great information guys, thank you!