I know someone here can answer this;
If I have a 5.56 AR and want to change to a 6.8 or 7.62 or etc..., I know the barrel changes, but is it the same bolt carrier group? what about mags?

Basicly, what parts (besides the barrel) are different?

I'm asking because I've never seen a 6.8 BCG or mag!
I do know a 308 needs the AR10 reciever - basicly a different rifle altogether.

This is just something that is running thru my thick skull!! LOL!!!

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Mags:
http://www.botachtactical.com/ba630ma.html

http://www.brownells.com/.aspx/pid=2...6-8mm-MAGAZINE

BCG:
http://www.spikestactical.com/new/z/...-68-p-472.html

For MOST caliber changes in the AR platform, you will need a new bolt (not bolt carrier), magazines, barrel, and maybe a heavier buffer to lighten recoil.

Some calibers like the 300 AAC blackout, 7.62x40 Wilson Tactical and perhaps a couple others use 5.56 brass and claim to use 5.56 mags. So with these calibers you would only need a barrel (possibly the buffer too).

TG

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TO THOSE WHO ENJOY THAT FOR WHICH THEY HAVE NEVER BLED, DON'T THANK THOSE WHO HAVE, THEY BLED NOT FOR YOU, BUT FOR EACH OTHER.

The 300 BLK only needs a barrel change. Same 5.56 bolt and mags work.
Dave N

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Independent Field Tester/R & D
"Better to die for something than Live for nothing"

Yes, basically you need just about a complete upper for the 6.8 and 7.62x 39 (different barrel and bolt) plus different mags. PRI mags work good in the 6.8. Like others have said some calibers will allow you to use 5.56 mags.