When you load light you don't get enough pressure to allow casing expansion to seal the cylinder , gasses are being blown backwards down along the OD of the casing and that's why you see soot. I would try loading right to max and see how that works.I shot some H110 today.
I noticed with 44 grains, it got everything dirty AF, down the cases, all the way to the rim. Pic below.
But as I increased the charge it wasn't an issue anymore. 45.5 shot great. .
The bullets are .452 230g FMJ from RMR.
Look at how dirty those fired casings are. Some have grains of powder stuck to the side.
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