What Jon said about proof. I have a Ugartechea 119 in 16 that is proofed to 900 bar, because that's standard for 16 gauge I think. I don't exceed the service pressure even though I have a hidden third bite for added strength. I think magnum proof is 1200 bar (see the other conversation on proof on the BBS). I think 12's are proofed to 850 bar for 2 3/4" chambers. But I also have a 3" Zabala Hermanos 12 proofed to 1000 bar, so not magnum proofed, but not standard proof.