Dave, I think your test is fine as-is. You should probably let it run for a good month, perhaps monitoring it at 3 day intervals (or whatever is convenient) and take some good pics as interesting things develop (if any).

And you might follow up this test with a degreasing and then do a spot burn of perhaps 4 powders in each section of barrel - then just let them sit in that warm environment while doing the same type of monitoring. Perhaps a half-teaspoon of powder in each spot. I think we pretty much already know what the powder test will produce though.