Some weeks ago, I reported the opinion of a highly skilled rifleman who said that you didn’t have to clean the bore of a match rifle until it had 300-400 rounds through it, and that a highly fouled barrel could even shoot better than a clean one. This, to me, is heretical, and I asked Dan Hanus MGYSGT/USMC/Ret., who built sniper and competition rifles for the Marines, and now is Production Manager for Bergara Rifles, what his take was:
“Some people believe that a dirty rifle shoots best. I don’t agree with that for a couple of reasons. First, a dirty bore has debris in it. As the bullet passes through the bore the debris scores the bullet, which in turn can cause turbulence. It’s the same as when pitchers would score a baseball with a nail file. Baseball outlawed the practice because it made the ball fly funny and the batter had a harder time hitting it.
“On the other hand you should always foul a bore because a bullet from a clean bore will have a different trajectory. But remember that ‘fouling’ can be as few as 3 shots.
“Second, as carbon builds up in the chamber, specifically the throat area, it’s going to change how the bullet jumps from the case mouth to the lands and grooves. If there’s too much carbon buildup, it can push the bullet back into the case, increasing pressure and changing the impact of the round. ‘Accuracy is derived from mechanical repeatability.’
“A dirty bore can increase accuracy in a shot-out rifle, but that’s in a .308 with more than 7,000 rounds through it.
“I think that 2500-3000 rounds as the maximum barrel life for a .308 is a bit premature. However, F-Class shooters use handloads that push the bullets faster than factory ammo, so it might apply in that case. However, I haven’t noticed any dropoff in accuracy from a ringer .308 we have here that has 5000 rounds through it and still shoots sub-1/4 MoA groups.
“Marine Corps policy was to clean the rifle after every use. We always used a good copper remover like Sweet’s 7.62. Snipers always fouled the bore with a few shots, so a clean bore was never an issue.”
So I guess I’ll keep cleaning barrels.