I’ve heard all of the barrel speed up in first few hundred rounds talk forever and I have noticed something since I have started cleaning my barrels with abrasives to the point of removing all of the hard carbon out, that they tend to speed up some around 70-100 rounds after cleaning. My question is, is barrel “speed up” due to the metal changing inside or is it due to hard carbon build up that most normal shooter don’t clean out and that increases the pressure?