Hi Mike,

Easy to tell, side by side, when new. But I have picked up some "Copper Rim" strikes on eBay that when I cleaned them, they had just tarnished a very nice reddish color but were actually regular brass rims. I've noticed that redder color a lot on strikes stored in Air-Tites with the white foam ring. There is a much higher copper content in the red brass, I think as high as 85% so I'm sure it has slightly different electrical conductivity and maybe a slightly different weight (specific gravity) but I don't know of any easy way to tell besides the color. Like Colin said, the Copper Rims are still brass, just more copper than normal yellow brass.