You shooting the 300gr RCBS makes me wanna try the lee 310. Seated long it would be pretty close to the rifling.
Problem is my lee 310 mold only cast a little over .430. A .431 sizing die might scuff 1 out of 10 bullets.
I know a 310gr bullet shouldn’t stabilize in a 1-38” twist but I like to see things for myself.
Don't own any 44 moulds over 265 grains..............don't need the recoil or the rainbow trajectory. Not hunting anything larger than whitetails. If I want to throw a big chunk of lead, I just use my Remmy 1100 slug gun. Surprised that Rick's 300 SWC that was HP'ed, weighs 301 grains, naked..........with my alloy.
Over, thirty years ago, I tried some commercial cast (Bull X) 300 grain LFP's in the Marlin. They had to be single loaded, accuracy wasn't that bad, IIRC............ but I'm not interested a single shot lever.
My gun will feed and cycle the RCBS 240 SWC GC, unlike many others. The RCBS 300 SWC doesn't balk, either, even though it's nose is significantly longer.
Right now, I waiting on a replacement mould from MiHec. Got in at the end of a Group Buy for a 44-250 RF HP (.434 dia)...............gas check shanks were undersized. Only checks that would stay on were Sage's aluminum for undersized shanks.............copper aren't offered. Expecting it soon, cause MiHa just sent an email, requesting my address.