Originally Posted by
montrala
100% no treatment during finishing in USA. But HK Gmbh is usually very tight-lipped about what they do to their barrels back at Oberndorf (and what alloy exactly they use to make those barrels).
Modern HK pistol barrels are supposedly also unlined... and I'm still to see rusting one.
Also my MR223 barrel, that is not chrome lined and spent last 3 years in humid basement (and cleaned from time to time, if I'm in the mood) is yet to show any sign of rust or wear (while add on equipment like muzzle device or screws on mounts show rust very fast).
Some friends put huge amount of ammo (like 50.000+) trough SL8 that has only chamber chromed and bore looks and shoots like new.
Anyway, if someone will cut MR556 barrel and have left of examined, I'm very interested in findings. Also some extreme rust tests can be performed on leftover.