At AccurateShooter.com many of the competitive shooters don't even like tumbling their brass using stainless steel pin media because it removes the carbon buildup inside the neck. From what I have read about it, the scrubbed brass causes uneven neck tension with the bullets. Some believe a metal to metal bonding is taking place between the bullet and case neck that increases over time. There is always a big debate over what case cleaning method is best to use with many leaving the insides of the neck alone.