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Full Auto BCG Ok, or Not ok

Discussion in 'General Firearm Discussion' started by jvbutter, Nov 27, 2014.

  1. jvbutter

    jvbutter Cornelius, Or Active Member

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    I was searching for a BCG for a build, I found a good deal on a new unit. However I got worried about it because it was full auto BCG. I did some searching and find that its not just the BCG that makes an AR a full auto gun. Looking at mine, the selector switch must be different also. I heard it was in the fire group that really makes it full auto or just single action.

    Is there anything wrong, with using a full auto BCG in a standard AR rifle?
    Is there any benefits of using full auto BCG in a standard AR rifle?
  2. Kruejl

    Kruejl Hillsboro Moderator of the Coriolis effect Staff Member Gold Supporter

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    Nothing wrong at all. A Full auto BCG can handle heat better and should last longer under sustained rapid fire. Most good builds include a full-auto BCG that is properly staked.
    3MTA3 and Caveman Jim like this.
  3. doobee8

    doobee8 Salem, OR Bronze Supporter Bronze Supporter

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    Its also supposed to increase reliability due to more bolt mass.
    Stomper, 3MTA3 and Caveman Jim like this.
  4. Mr Smith

    Mr Smith 54 68 65 20 73 74 69 63 6b 73 Active Member

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    Here is the difference between the two:


    I have a full auto BCG in my build.

    A full auto BCG does not and will not ever make your gun full auto, nor is there any law against running one in a semi auto weapon.

    to make a gun full auto and not legal:

    you would need an M16 selector switch


    A select fire or m16 fire control group

    note the notch on the end of the hammer... this is where the auto sear catches the hammer to hold it back until the bolt comes back forward to the near closed position and slaps the auto sear release lever to release the hammer.
    note the open slot on the trigger. This is for the full auto disconnector which is significantly longer than a semi auto disconnector. The longer disconnector allows the M16 selector switch to push the disconnector downward out of the way for full auto operation. While this disconnector is out of the way: the auto sear and notch at the top of the hammer get used to time and control the full auto fire rate by the auto sear acting as a temporary disconnector which holds the hammer back until the bolt is closed.

    And finally the auto sear -

    this is a M16 auto sear which would require the 3rd FCG pin (not present on AR-15's) to hold the auto sear in place.

    pic also shows the cam for burst fire on m16's that had a 4 position selector (safe - semi - full - burst)

    or for full auto AR-15's the drop in auto sear
    or lightning link
    note the lightning link requires a special double disconnector select fire trigger and uses a standard AR-15 hammer as the second disconnector acts as the full auto temporary disconnector until the carrier pushes on the lightning link lever which pulls the second disconnector out of the way to release the hammer.

    The full auto carrier is the only part you are legally allowed to have and use in a semi auto weapon.

    any other part of the m16 or ar-15 FA conversion fire control groups is not permitted unless they are a preban registered part which in WA state is still not legal to have either, however it is legal in oregon if you have a registered drop in auto sear, registered M16, or registered lightning link and the tax stamp that goes with them. However if you are the lucky owner of one of those: then you can legally buy and possess any M16 fire control component.
  5. Flopsweat

    Flopsweat Slightly right of center Well-Known Member

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    Mr. Smith, that is the best description of M16 vs. AR15 FCG that I have read. Bravo!
    Mr Smith likes this.
  6. AMProducts

    AMProducts Maple Valley, WA Jerk, Ammo Manufacturer Silver Supporter

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    One thing not mentioned... a standard AR-15 lower will not accommodate an autosear, the difference between an AR lower and an M-16 lower are substantial, the pocket is nearly twice the size. If you look carefully at the cam settings on the selector lever, it's much wider than that on a normal AR.

    So any discussion of "constructive intent" also requires a machine shop with at least a mill.
    Brutus57 and scrandall01215 like this.
  7. Nickb

    Nickb Moxee Active Member

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    Very informative Mr. Smith.
  8. Stomper

    Stomper Oceania Rising White Is The New Brown Silver Supporter

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    Another thing of note in the FA/SA BCG comparison is that the bottom of the SA BCG is (typically) "ramped" where the firing pin is, so that the hammer "rides" up and around the BCG "softly" so as not to strike the firing pin with a solid blow should the SA sear not catch the hammer for some "unexplained reason". :rolleyes:
  9. deen_ad

    deen_ad Vancouver, WA Well-Known Member

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    < Why they don't have school shootings in Israel.
    Notice the long gun slung over the teachers shoulder?

    Any automatic parts are totally illegal to even possess in WA but still a good thread!!

    NRA Life Member, Benefactor Level
    "Defender of Freedom" award
    NRA Golden Eagle member
    WAC member

    "Having a gun is like a parachute, if you need one and don't have it you may never need it again"
  10. Brutus57

    Brutus57 Skagit County Well-Known Member

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    Dammit, I hate it when I run out of printer paper....

    Brutus Out