Spomer ain't really my cup o' tea, but my experience mirrors his, with several rifles- some factory, and some custom.I've moved into the don't clean camp. It hasn't failed me yet.
I'm still curious about the copper on top of cup/core fouling cleaning theory Spomer came up with. Supposedly, it's a thing. I can't confirm as I don't switch loads in a gun when it's shooting well.
Start with a clean bore, Barnes shoot great. Switch to cup and core bullets, shoot great. Switch back to Barnes, shoot like crap. And continue to shoot like crap until I clean the barrel. Don't have to remove every spec of fouling, but have to get it "pretty clean".
I dont know why this happens (at least in some scenarios)- but i do know that Barnes Bullets are 100% copper, and the gilding copper used for bullet jackets contains between 5 and 10 percent zinc.
I've even seen it take a couple shots to settle down (both velocity and precision) when switching between different cup and core bullets
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