Mike George

Plastic fouling usually shows up as a grey film over the bright metal of the barrel and, as it is acidic, it should be removed as soon as possible.

It usually comes out with ordinary cleaning solvent on a bronze brush.

I once had a gun which, for some unknown reason, was particularly prone to plastic fouling and I discovered that, if the fouling is particularly obstinate, a squirt of Hoppes No.9 rifle barrel cleaner does the trick.

If you have to resort to this tactic, remember to wash the bronze brush carefully afterwards, because Hoppes attacks all alloys containing copper.