I have just started trying cast loads in my 1949 Long Branch Mk 1*.
So far I have onlytried bullets made from the 185 gr Lee mold sized .312. IMR3031, 20 gr gave me 2"-2.5" @ 50 yds with iron sights (ladder type). I fired 3 shots with the battle sight for a 1.5" group. I also tried Trail Boss, 7-8.5 gr. The best was 1.5" @ 50 yds with 41 gr. Lots more powders to try but this is the first LE I've had that would shoot these bullets with any accuracy. Most key-holed in my P-14's.
For a fun plinking load , try Hornady 85 gr HP/XTP pistol bullets (.312) with 40 gr of H4895. I loaded up 5 last week and got a 1.4" group @ 50 yds, but 4 of those were in .5" with iron sights. I loaded more to try next trip to the range.