karlkurtz32 0 Posted December 1, 2013 The side of my barrel says: P 5.56 NATO 1:7 Hammer Forged/CL Does anyone know what the letter P means? Quote Share this post Link to post Share on other sites
Vzguy 13 Posted December 1, 2013 Quick search revealed that P could mean Elisco Tool, which was in the Phillipines. They made barrels for Colt. Quote Share this post Link to post Share on other sites
302w 83 Posted December 2, 2013 Probably either proof or particle. My Colt A1 barrel has MP for magnetic particle tested. Quote Share this post Link to post Share on other sites
Fishpaw 17 Posted December 2, 2013 Historically it means Proofed. They will shoot a special high powered proofing round through it to test the strength of the barrel. If it can take the pressure of this special round, it will easily take the pressure of a standard round. Quote Share this post Link to post Share on other sites