I can't speak to much of the OP's test. Except it sounds like a good day at the range! But I can speak to the "dirty" 2400. I have been shooting 2400 since the mid 1960s. With loads that were Phiffle to more powder than most sane people would shoot. From 38 spc. to 44 mag to reduced rifle cast loads and I have never been able to not have powder(or as I like to call it---Gravel) left on and in the gun and surrounding area. Once, after shooting several hundred 38/357 loaded with 2400 on a concrete shooting area, it was necessary to sweep the area in front of my shooting spot because it was like someone had sanded that area and it was slippery. Sort of like walking on marbles or small ball bearings.