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View Full Version : .223 Marked Upper - 5.56 Ammo


Aldemar
05-02-2012, 11:16 AM
I know the calibers are 99.9% similar. However, could a .223 marked lower cause any legal issues when using 5.56 marked ammo (or the other way around)? Say a LEO is looking at your AR for some compliance issue. He notices you have a .223 marked lower but are using 5.56 ammo. Is this something that needs to be concerned about?

Actually, why is the lower marked at all?

dantodd
05-02-2012, 11:18 AM
not an issue legally.

dsmoot
05-02-2012, 11:23 AM
Not a legal issue. Only concern is that you should not use 5.56mm ammo in a .223 marked upper because of the differences in pressure.

stix213
05-02-2012, 11:37 AM
The legal issue would be if the gun explodes and injures someone else, which would then be caused by negligence on your part for using ammo that produces higher pressures than your gun was designed for. That would be for an upper marked .223 though. Lower it doesn't matter. (you are saying upper in one place and lower in another, so not sure what you mean)

mrdd
05-02-2012, 11:49 AM
I know the calibers are 99.9% similar. However, could a .223 marked lower cause any legal issues when using 5.56 marked ammo (or the other way around)? Say a LEO is looking at your AR for some compliance issue. He notices you have a .223 marked lower but are using 5.56 ammo. Is this something that needs to be concerned about?

Actually, why is the lower marked at all?

The lower must be marked by the manufacturer as required by 27 CFR 478.92 (a) (1) (ii) (B) and (a) (2).

NotEnufGarage
05-02-2012, 11:53 AM
The legal issue would be if the gun explodes and injures someone else, which would then be caused by negligence on your part for using ammo that produces higher pressures than your gun was designed for. That would be for an upper marked .223 though. Lower it doesn't matter. (you are saying upper in one place and lower in another, so not sure what you mean)

Yep... Shoot all the .223 you want out of a 5.56mm upper, but don't be shooting 5.56mm rounds from a .223 upper unless you enjoy breaking things.

.223 - max pressure = 55,000 PSI
5.56mm - max pressure = 62,366 PSI

An older, neglected, or damaged .223 could be comprimised by the higher pressure.