I normally only reload one or two hundred cases at a time, but yesterday I reloaded almost 1200. My charge weight was 10.00 gr. and my Lee Auto Drum powder measure usually throws charges with this powder +/- 0.06 gr. I checked it four or five times before I started loading and it was throwing charges like 9.94 gr to 10.02 gr.
After almost 400 rounds, I checked it again. It was throwing 9.6 gr. My mistake for not checking sooner. Fortunately, it drifted down rather than up. I wondered if the near-empty powder hopper was putting less pressure on the drum, but after I filled it to the top, it was still throwing light charges. The powder is a coarse ball powder that should behave well. I don't think it packs down or fluffs up like a large flake or fine ball powder. I screwed out the adjuster and carried on. I checked the charge more frequently after that but found I had to adjust it twice more before I had loaded them all.
I speculated that maybe the inertia of the drum rotation was gradually knocking the adjustment in, but I'm not convinced of this. I'll have to put white marks on the drum and screw and see if it's drifting there or if the volume of the chamber is not changing but something is changing with how it fills.
Any other ideas why it might have done this or what else I should look for?
After almost 400 rounds, I checked it again. It was throwing 9.6 gr. My mistake for not checking sooner. Fortunately, it drifted down rather than up. I wondered if the near-empty powder hopper was putting less pressure on the drum, but after I filled it to the top, it was still throwing light charges. The powder is a coarse ball powder that should behave well. I don't think it packs down or fluffs up like a large flake or fine ball powder. I screwed out the adjuster and carried on. I checked the charge more frequently after that but found I had to adjust it twice more before I had loaded them all.
I speculated that maybe the inertia of the drum rotation was gradually knocking the adjustment in, but I'm not convinced of this. I'll have to put white marks on the drum and screw and see if it's drifting there or if the volume of the chamber is not changing but something is changing with how it fills.
Any other ideas why it might have done this or what else I should look for?