That winchester factory load looks like a really good one I would take one of those apart to see if you could mimic it When it comes to steel that's what you need is high speed
It was a pretty good. I am sure all factory steel loads use Alliant Steel powder. I was finally able to get some Alliant steel and am getting good speeds and patterns.
Try the same federal hull with the MG42, 1 oz of BBs and 32gr of LS and see what you think, should be lower 1400 speed. You can go up more grains on the LS but I've found the wad start to wear through a little at charge weights that are higher...I haven't tried any mylar wrap though.
