"If it's brand-new, why would it need to be cleaned? You don't have to clean a new barrel." That's the advice some Internet sages have been throwing around. But we know the value of a lot of the info on the Internet! Is this good advice? NO, say Brownells Gun Techs™ Steve and Caleb, and they've got out the borescope to show us why. An internal tour of a factory-new AR-15 barrel reveals a coating of grease in the bore and, more importantly, in the chamber. If the grease is thick enough, it'll prevent the case from extracting after firing, leading to a jammed gun. The grease can also constrict the chamber, causing excess pressure leading to excess bolt velocity, which results in a malfunction, too. Worst-case scenario, the grease obstructs the bullet's travel through the bore and causes to a blown-up gun, the dreaded and very dangerous KA-BOOM!
So this myth is handily BUSTED. You do have to clean a new barrel, whether it's a replacement / upgrade or part of an entirely new gun. Run a cleaning patch soaked in solvent down the bore. You don't need to get out the copper solvent or scrub until your arm aches. You just want to remove any grease that was put in the bore and chamber to protect them during shipping / storage. That simple cleaning is the best way to be sure there is nothing in the bore that shouldn't be when you fire that first round.
Caleb Savant
