Something of a disappointment, but...

[Ballistics in Scotland]

I bought some of these on eBay, only to find out that they are steel, and too thinly plated to avoid steel to bore contact. How bad is that? It might even polish a frosted bore. They are actually about .370 ID and .389 OD.

http://www.ebay.co.uk/itm/371223881016?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649

[goblism]

I would toss them, not worth damaging a barrel to save a few bucks on jackets

[runfiverun]

some steels are less abrasive to a barrel than copper.

[xman777]

Choot em'! I put all types of schmoo down my barrels and test things out. My favorite is steel 209 primer cups in the 223.

Obviously don't use your trophy rifle.