Has anyone experenced the same thing? I can't get the brass to take a polish in my tumbler. The base by the primer will polish, but the rest will stay dull.
Other brass will polish, but not the 5.7.

the problem is its laquer coated, for lubrication in the firing chamber

http://fivesevenforum.com/forums/showthread.php?t=389&page=1&pp=10