For high velocity .22 I prefer copper washed ones, for standard velocity I prefer lead .22.
I noticed that if I use high velocity lead .22, they leave too much lead in the barrel, while standard velocity ammo does not. I suspect that copper wash allows higher melting point, thus barrel does not lead as much with high velocity .22. Without any experimentation, just my guess, velocity is the key factor in lead vs. copper wash .22 bullets. All high quality .22 LR ammo used in Olympic competition are standard velocity.
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