What Cal Uppers will work with a 5.56 lower?

[Drivedabizness]

Been told (won't say by who) that a 6.8 upper will work on a standard 5.56 lower.

I assume .243 would too.

What other "hi power" upper would work on a standard lower?

Thanks. I have looked a lot and not seen this elsewhere on the forum.

[Just-in]

You were told wrong. I hope that didn't come out like an ******* but yeah a 6.8 upper a 7.62x39 hell theres even .50 uppers that will pin to a .223/5.56 upper.

[707electrician]

I would think that anything with an OAL less than or equal to a .223 would work

[eaglemike]

If you want to use a magazine that fits in the magwell, the overall length listed above is correct. A .243 is too long, 6.8SPC works fine.

If you use a bolt action upper single shot, pretty much unlimited as long as it's legal.

I don't know if anyone has developed a bolt action repeater upper for longer cartridges - such as using a side or angle mounted magazine. I've not done any drawing to see if it could be done, but seems like an interesting concept.

[707electrician]

If you want to use a magazine that fits in the magwell, the overall length listed above is correct. A .243 is too long, 6.8SPC works fine.

If you use a bolt action upper single shot, pretty much unlimited as long as it's legal.

I don't know if anyone has developed a bolt action repeater upper for longer cartridges - such as using a side or angle mounted magazine. I've not done any drawing to see if it could be done, but seems like an interesting concept.

I think I have seen a bolt action .50 cal upper with a side mounted mag