have run a 16" lightweight JP barrel for last 2 years. going to build one in ultralight now. don't worry about the thermal junk. it's a JP barrel, it will flat out shoot.
seems inconsistent with MG rules. for example, with pre-load tables we are actually loading shotgun tubes with live ammo. checking yer optics was never an issue.
9 x out of 10 it won't matter. you could go thru the trouble of slugging the barrel, but it aint worth the effort. if it's lead, .401 in most cases...YMMV.