I shoot three of these, and only one so far does well with cast bullets. It's a Loewe that has been sporterized with 24" barrel, shortened stock and an old Weaver KV scope, with post and cross hair. It is the only one of the three that slugs close to .312, the other two being closer to .3125. My Lyman 311284 casts a bullet of modern #2 alloy (92-6-2) right at .312, and the rifle shoots about 1.5"-1.75" for five shots. Bullets are sized .312, mostly to properly seat the gas check. Lube is alox/beeswax.
So far two powder charges have worked well, 12.0 grains of Red Dot, and 35.0 IMR 4064, both ignited with old Winchester 111 Large Pistol primers.
As I shoot this rifle more, the groups are tending to the upper end of the size range, and I think it may be time to lap out the mold and get a new .313 or .314 sizer.
Have you tried the Lyman 314299? Maybe if Midsouth makes available the .316220 in the limited production Lee molds in the future, it would be a good bet.