LOL!! I think my train of thought is going to run in a complete circle, so if ya'll will bare with me through this. If you equate a new gun to a new or newly rebuilt engine, you're both right even though on opposite ends of the "break-in" spectrum. In a new engine, or gun, the first 500 miles or rounds, ya don't really want something super slick, it will impede the normal smoothing of newly machined surfaces from friction and wear. The engine needs a single viscosity petroleum oil so that the rings and bearings can "seat", the new gun will benefit from no lube or even a mild abrasive. My preference is valve lapping compound, but the toothpaste will work. Back when I was still flying, my crewchief's used "Pearl Drops" tooth posish to remove scratches on the plexiglass windscreens. They believed the tooth polish to be a little more agressive than regular tooth paste. Then each (engine and gun) needs to be flushed and a high quality lube applied (STP being a "Super Slick" additive of old) to reduce the friction between the moving parts.