Mike, I have not loaded any sort of .41 mag loads, whether lapping or not, but have lapped both the .357 and .45 Colt with Bullseye.
As best I recall the .357 lapping loads were 1.5 grains of Bullseye and the .45 Colt loads were about 2.5 grains. Given that the .41's capacity is somewhere in between, the starting load should be in between also.
I'd start with 2.0 grains and see how that went. You might stick a bullet in the bore a time or two. I'd guess that Red Dot loads would be nearly the same, within a tenth of a grain or two, but haven't tried that powder myself.
I also seat the bullets backwards, flush with the case mouth, to minimize the powder space. Good luck.
A forum community dedicated to Sport shooters, owners and enthusiasts. Come join the discussion about optics, hand casting bullets, hunting, gunsmithing, styles, reviews, accessories, classifieds, and more!