Received our new Criterion barrel in 20 Practical from Jim the other day.

After shooting 200 rounds through the gun, being very careful with break-in, I have yet to see any copper out of this barrel.

Using Barnes solvent, a nylon brush and a coated rod. At most, and even this is iffy, some of the early patches may have had a very light blue/green tint. Other than that, nothing.

Shooting 39gr SBKs and 40gr Vmax fwiw.