Fire two shots through any barrel and a patch with an ammonia based cleaner will come out blue. This is a result of copper in the barrel but not necessarily copper fouling. With each shot, some bullet jacket material is left behind. In a good barrel, this amounts to nothing more than a wash which though it may show some colour, has no measuable dimension. This wash does no harm and may, in fact, be beneficial. Copper fouling begins to be a problem when it builds up in the bore and does have dimension. At this point, it will cause pressure spikes and may also damage the bullet in subsequent shots. Accuracy will deteriorate badly. Sometimes, such fouling is relatively easy to remove. Other times it may take considerable time and effort.
I am not a fan of counting on a chemical reaction to tell me if there is copper in my barrel because the copper is always there. My concern is excessive copper and I can see that (although I do need some optical aid now).
If a barrel fouls badly and accuracy falls off after just a few rounds, I like to try and cure the fouling problem rather than just clean often. This may mean lapping or polishing the barrel or running through a break-in procedure. Leeper
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