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Discussion Starter #1
still new to the ar15 stuff.

I have a 556 upper, and 300acc upper to go with my local shop made 'm4' milspec style lower.

at a show the other day i saw a lower that a guy was selling calling it a multi caliber, ( lower had that printed on it.. multi cal.. etc. ) and said that was what you had to have to change out upper's of different calibers?

?????
 
G

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It is just a way or marking them. Some people put multi cal on them so you don't have a 300aac that says 556 nato on the side of it.

As long as the round you are using can fit in the same mags used as a 556 then you can use any lower with just about any upper. The only ones are the large pin Colt uppers and lowers.
 

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Discussion Starter #3
that's what I thought.

the 300 acc and 556 fit the same mags and no issue. my buddy has a 762x39 upper on a colt lower and he had to buy special mags.. but otherwise no difference in function.. which is why i wondered.

so it's just a marking designation so that your lower isn't marked with a caliber specific..e tc.

thanks
 
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I think the mags for the 7.62x39 are different because of the body taper of the round. Look at an AK mag and how curved they are compared to our AR mags.
 

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Yep, RRA is making an AR47 lower that uses AK style mags for thier 7.62X39 uppers.
 

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Discussion Starter #6
i saw those.. but that pretty much limits you to that cartridge in that lower it would seem.
 
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