Copper fouling - why does it affect accuracy?

Well, for one it doesn't allow the rifling to get a good bite into the bullet as it is traveling down the barrel. I guess that it also has to do with the fact that when your barrel fouls the diameter shrinks and I think that it changes the pressures in your barrel. These are just my guesses.
 
Well, there are a couple of reasons: 1) The copper fouling can elevate chaber pressures, in effect, changing the load. 2) If the copper fouling is bad enough, it can distort or damage the bullet jacket.

I am certainly not an expert, but these are the two theories that I have beleived.
 
I agree with a lot of what has been posted

fouling is rough,..and therefore affects the rotational forces. The jacket will take the brunt of that force. As the bullet exits,....it will be out of balance,..etc etc etc. The resulting effect is what pilots call "yaw"

Also,..yes gas pressures are increased,..therefore changing both the harmonic frequency, and the muzzle velocity. This is why your accuracy falls off,..you are no longer in "the node" and need to change something in your mix,..and since the load and the rifle are the same,..it stands to reason the change needs to be a bore cleaning as a direct result of fouling.
 
If the copper is thicker early on in the barrel, then it would force the bullet to be smaller, maybe looser in the barrel? After using Moly-Fusion I no longer get any copper fouling, only powder.T.20
 
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