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Swapping BCG in ARS

Discussion in 'Rifle Discussion' started by buyamonkey, Jan 17, 2010.

  1. buyamonkey

    buyamonkey West vancouver WA Member

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    Hi folks,
    I'm just looking for some advice from some of you who have been shooting ARs over the years. I have a factory built upper on it's way and I want to try a brand new Young Manufacturing NM BCG (that I already have) in it. Should I be concerned about swapping Bolt Carrier Groups between guns or is that only a potential concern a couple thousand rounds down the road? I don't know a whole lot about head spacing and as usual the "interweb" has some conflicting reports about the level of risk with not checking first.

    Getting some "go," "no go" gauges are on my list for future projects, but I'm leaning towards new BCGs and a factory built upper are going to be fairly safe.

    Thanks for your input.

    Eddie
     
  2. xjjeeper223

    xjjeeper223 Medford Active Member

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    Typically...

    New Upper + New BCG = OK

    Old Upper + New BCG = OK

    New Upper + Used BCG = Check and Measure
     
  3. GUNNY

    GUNNY DAMASCUS OREGON Member

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    Dont swap bolts, youre bolt wears grooves in the lower receiver and the bolt it self when you swap them the grooves dont match and the result is faster wear, as for the guage ar's are self headspaceing spend the cash on ammo
     
  4. eldbillbo

    eldbillbo clackamas New world samurai and a redneck none the less Bronze Supporter

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    Maybe someone in your area has a set of gauges you can check yours with to be on the safe side its very rare to have issues unless buying a shot out barrel or very used bolt but better to be safe than sorry.

    if you plan to do a lot of swopping of bolts just buy the gauges they are fairly inexpensive for the peace of mind you will get.

    Gunny not sure what you mean by your reply, the bolt does not ware anything in the lower receiver
     
  5. Trlsmn

    Trlsmn In Utero (Portland) Well-Known Member

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    :bsflag:
     
  6. SlickJoeSD

    SlickJoeSD Astoria, OR Member

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    Where are these grooves? I don't have any on mine nor the bizzillion year old M16's @ work in the .mil.

    :huh::huh:
     
  7. MacBookProAR

    MacBookProAR Stayton Member

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    This

    seriously... auto head spaced? :laugh:
     
  8. Schwabdl

    Schwabdl Hillsboro Active Member

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    guess that my gauges were a big waste of money
     
  9. buyamonkey

    buyamonkey West vancouver WA Member

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    Thank you guys. I don't know what I'd do without the internet. I'd have to hang out at ranges, gun shops and seedy bars to get this kind of input. :)

    I think I'm going to still get a set of gauges for when I build up my own upper.
    I'll let you know if things don't go as planned when I pull the trigger.

    Thanks again
     
  10. madcratebuilder

    madcratebuilder Ardenwald, OR Well-Known Member

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    Well worth the peace of mind not to mention the avoidance of injury.



    :bluelaugh::laugh::bluelaugh::laugh::bluelaugh::laugh::bluelaugh::laugh:
     
  11. NoAim

    NoAim Hillsboro, OR Active Member

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    Okay, I'll jump in. I think Gunny's heart is in the right place, but some of his facts aren't.


    The AR-15 has a non-adjustable headspace. The headspacing is set via the barrel extension and the bolt as it locks in.

    So, as the gun us used and fired, the bolt head lugs rotate against the barrel extension lugs. Over time, this can cause some wear. If there's enough wear, headspace will increase, although it usually takes a looooong time.

    With a new AR, the headspace has already been set from the factory via the barrel extension. The fun comes when you start using a really old bolt. This bolt may have worn excessively, and thus has increased the headspacing.

    Typically, unless you are using an old bolt and an old barrel, this won't be a problem.


    In short, yes you can swap them back and forth. But remember that you'll be putting more rounds on the bolt than the rifles.

    If you want to be sure and not worry, a new BCG is only about $150.
     
  12. PromptCritical

    PromptCritical Oregon City, OR Member

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    But as I recall, the carrier is irrelevant to headspacing so you should only need a new bolt if you need anything at all, and those are pretty cheap, like $40 or so.

    I agree about gunny. Seems the only real error is terminology. Replace "lower receiver" with "Barrel extension" and he's technically right, aside from the part about automatically headspacing, which could also mean that the headspace isn't adjustable.

    And this being the internet means that any argument involves ignoring the forest and concentrating on the trees, so it is very important that your trees be straight and correct so that the shape and size of the forest is the center of attention.
     
  13. NoAim

    NoAim Hillsboro, OR Active Member

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    Thanks. That had totally slipped my mind. Yes, you could just swap bolts and have less outlay of money.

    This headspacing is typically why you see high end AR barrels also sold with a "matched bolt".
     
  14. madcratebuilder

    madcratebuilder Ardenwald, OR Well-Known Member

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    That was poor taste on my part, god knows I've said some dumb things on the internet and it well live for ever. Sorry Gunny.