I have been experimenting with a 32-40, using an existing Martini Cadet barrel, that slugs at .320" at the muzzle.
I made a plain, nose pour mould and the boolit is 180g, cast from 30-1, Pb-Sn alloy. Nice and soft.
I tumble lube the slick boolit, in 45-45-10 LLA-Beees wax-Turps, lube. Some I knurled, by rolling them under a bastard file, on a wooden surface. They don't shoot any better than smooth lubed boolits.
Warm everything up and tumble, then let dry on baking paper. The lube is quite hard and very thin.

My top pour PP style mould, 3 knurled boolits on left and 3 straight out of the mould.

I have also tried a .320" ball load, but the Nobels powder I used, was bad and didn't burn well.

This 4 round target was shot at 50m. Rifle was fitted with a Red dot sight.
Load is 8g of ADI AP70, behind the 180g tumble lubed slick. Estimated speed is 1350fps.

I fired the last three rounds that I had left, at a target at 100 yds and the group measured 1.2"
I consider this experiment a resounding success