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Sharing BCG between 2 ARs

Diver43Diver43 Senior MemberBetween Ft Lauderdale and MiamiPosts: 12,561 Senior Member
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?
Logistics cannot win a war, but its absence or inadequacy can cause defeat. FM100-5

Replies

  • breamfisherbreamfisher Senior Member Living in a van, down by the river.Posts: 14,038 Senior Member
    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.
    I'm just here for snark.
  • JKPJKP Senior Member North FloridaPosts: 2,678 Senior Member
    Yes.

    But don't mistakenly put a BCG from a piston gun into a DI gun and expect good results....
  • JayhawkerJayhawker Moderator Manistee Natl ForestPosts: 18,289 Senior Member
    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...
    Sharps Model 1874 - "The rifle that made the west safe for Winchester"
  • softwarejanitorsoftwarejanitor Member Posts: 241 Member
    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.
  • Diver43Diver43 Senior Member Between Ft Lauderdale and MiamiPosts: 12,561 Senior Member
    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.
    Logistics cannot win a war, but its absence or inadequacy can cause defeat. FM100-5
  • jbp-ohiojbp-ohio Senior Member Pensacola, FLPosts: 10,829 Senior Member
    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.
    "The democracy will cease to exist when you take away from those who are willing to work and give to those who would not." Thomas Jefferson
  • JasonMPDJasonMPD Senior Member Posts: 6,583 Senior Member
    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.
    “There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.” – Will Rogers
  • Tom MixTom Mix Member Posts: 101 Member
    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.
  • JasonMPDJasonMPD Senior Member Posts: 6,583 Senior Member
    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.
    “There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.” – Will Rogers
  • LerchessLerchess Senior Member Posts: 550 Senior Member
    It'll work fine as long as the bolt headspaces in both barrels.
  • BigslugBigslug Senior Member Posts: 9,698 Senior Member
    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.
    WWJMBD?

    "Nothing is safe from stupid." - Zee
  • Diver43Diver43 Senior Member Between Ft Lauderdale and MiamiPosts: 12,561 Senior Member
    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.
    Logistics cannot win a war, but its absence or inadequacy can cause defeat. FM100-5
  • breamfisherbreamfisher Senior Member Living in a van, down by the river.Posts: 14,038 Senior Member
    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...
    I'm just here for snark.
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