I hunt with ChamberMates 12/20 with black powder in a hammer gun, and they work just fine. The only problem has been getting the ChamberMates out of the gun for cleaning, because I didn't have the ChamberMates removal tool. Took lots of fiddling with rods and cleaning gizmos.

I have Lil Skeeters in 16/28 but have not used them yet. They are for those times when I can't find 16ga ammo.