223\5.56 chamber pressure...

[Gargamel]

My latest AR build is a conglomerate\Frankenstein of different parts, so I have a question.

I have read (damn internet) that due to chamber pressure, it is ill advised to run 5.56 ammo in chambers specc'd to .223, but the reverse is fine.

2 questions:

1. Is it just the barrel affected here or is the upper receiver also something to be checked out?

2. Is there any "easy" way to check the current chamber's application? (stamp on barrel?)

[GhostTX]

Yes, there should be a stamp on the barrel:

[black2002ls]

It won't affect the upper receiver. IT is specific to the barrel and extension.