6.8 vs. 5.56 stripped lowers

B

Bullcoop

Inactive
If you had a completely stripped AR 6.8 lower in your right hand and an AR 5.56 in your left is there any difference?
I ask because I've read 2 things that seem contradictory. First I read that you could switch uppers from a 556 upper to a 6.8 upper strait across w/no changes to the lower. Then as I was thinking of doing the build myself I noticed they sell 556 lowers and 6.8 lowers (both stripped).
If the only diff was in the upper (barrel, bolt, charging handle) then why sell 2 different lowers? Is it because they mark the lower 5.56 or 6.8? Is that the only diff?
Thanks.
BC
 
My understanding is just that - the only difference is the marking.

Kinda makes sense if you're manufacturing them for sale to make sure nobody puts a .223/5.56 round in a 6.8 barrel, or tries to do the same the other way around.
 
The only difference is the roll mark on the side of the lower. The only difference between a 5.56 and 6.8 AR is the barrel, bolt and mags.
 
The caliber marking on the lower has nothing to do with what barrel is mounted on it. If the loaded cartridge is less than about 2.280", it will feed in a magazine and the barrel is likely available from somebody.

Mine's marked multi-cal, but it doesn't mean the barrel is. It does mean I could set up about four dozen different uppers and shoot all of them with just the one lower. Some have done exactly that - but EBRD takes over and they morph into complete guns.
 
Markings is the only difference.

I had a 5.56 lower on my 6.8 SPC upper for a bit but decided to change it out with a bonefide 6.8 marked lower.
 
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