Sharing BCG between 2 ARs

Diver43

A co-worker asked me a question about AR-15s today, and I honestly did not know the correct answer.

If a person were to have say one lower and two different uppers, I know they can easily be changed. Now add to that the option that one is a 5.56 upper and the other say a .300 BO. I know that again you can just change uppers and are ready to shoot. However, his question is:
Can the BCG be removed from one upper and used in another?

My first thought was Yes, however after thinking about it, something is telling me that this is not a good idea.

The easy answer is telling him to quit being cheap and just have the two complete uppers, if you are unable to swing two complete guns, but I know the first thing he will say is; why not?

Any specific reasons that I can tell him?

breamfisher

In theory, it should work. .300 BO and 5.56 bolt specs are the same, and assuming reputable manufacturers they should interchange.

Logistically it's easier to have one for each upper, keeps your from forgetting it at home if you only take one to the range.

JKP

Yes.

But don't mistakenly put a BCG from a piston gun into a DI gun and expect good results....

Jayhawker

Theoretically, it should work...however, I have seen a BCG swapped from one perfectly functioning .223 upper to another .223 upper not work...don't have a clue why, but that's what happened...

softwarejanitor

It will usually work without any problems... however, many people believe that swapping BCG from one upper to another will cause the BCG and possibly both uppers to wear faster than if each upper had a dedicated BCG that was "worn in" to it. I think that this theory may have some merit but I haven't seen any conclusive studies that prove it.

Diver43

I guess that is the idea behind MILSPEC. Put them all in a pile and just grab pieces and put them back together.

I thought for sure something said that fittings change to grooves and such. Maybe I'm wrong.

jbp-ohio

Diver43 wrote: »

I guess that is the idea behind MILSPEC. Put them all in a pile and just grab pieces and put them back together.

I thought for sure something said that fittings change to grooves and such. Maybe I'm wrong.

:that: It was designed to work.

JasonMPD

Diver43 wrote: »

A co-worker asked me a question about AR-15s today, and I honestly did not know the correct answer.

If a person were to have say one lower and two different uppers, I know they can easily be changed. Now add to that the option that one is a 5.56 upper and the other say a .300 BO. I know that again you can just change uppers and are ready to shoot. However, his question is:
Can the BCG be removed from one upper and used in another?

My first thought was Yes, however after thinking about it, something is telling me that this is not a good idea.

The easy answer is telling him to quit being cheap and just have the two complete uppers, if you are unable to swing two complete guns, but I know the first thing he will say is; why not?

Any specific reasons that I can tell him?

Bolt carriers, yes. No issue. The carrier has no bearing on the head spacing of the bolt/barrel combo.

Tom Mix

The appeal of the 300 blackout to me is that that only difference in an 5.56 and 300 blackout rifle is the barrel, everything else works including the magazine.

This does not mean things do not need adjusted in order to work.

Actually I do not know the answer but I did want to be active in a post today.

JasonMPD

Tom Mix wrote: »

The appeal of the 300 blackout to me is that that only difference in an 5.56 and 300 blackout rifle is the barrel, everything else works including the magazine.

This does not mean things do not need adjusted in order to work.

Actually I do not know the answer but I did want to be active in a post today.

You got it.

It's fun suppressed, too.

Lerchess

It'll work fine as long as the bolt headspaces in both barrels.

Bigslug

Lerchess wrote: »

It'll work fine as long as the bolt headspaces in both barrels.

THIS

In 5.56mm anyway, the AR makers have proven VERY good at producing a system that allows you to play "musical bolts" between different rifles without headspace issues. The Lego Block nature of the system kind of forces them to be. At the very least, I'd be fairly comfortable swapping Bushmaster to Bushmaster, Colt to Colt, etc... Even so, I'd sooner drop a FIELD or NO-GO gauge in the alternate chamber and check rather than take someone else's word for it. It's one of those things that's always right. . .right up until the point that it's wrong. Once that's been verified, party on.

Diver43

Thanks to all for your input.
For some reason I had it in my mind that with two different calibers the bolt should not be switched.

breamfisher

Well... it depends.

7.62x39 has the same rim diameter as 6.5 Grendel and .50 Beowulf. But you can't change bolts between them because one bolt is cut shallower than the others. Can't remember which, and really am not bothered enough to look that up...