unspellable: As I recall, the bullet diameter (jacketed) on the 30 Luger is .310 - at least that is what I recall being miked out from Winchester bullets.
None the less, the importance of matching the bullet to the bore diameter is quite important. Firing a .308 bullet down a .310 tube isn't gonna get you a lot of accuracy but, you may wish to look at current offerings in 308 bore, as they quite often need to be sized down after dropping from the molds at a larger than bore diameter.
The 30 Luger is going to be finicky with almost anything short of a round nose bullet, unless yours isn't picky about what it will digest (however, that bottleneck design is very forgiving on bullet designs, and you may find that even SWCs feed reliably). Years back, some of us used to bong the gong on the silly-wet range with 30 Lugers shooting the 110 gn 308 HP for the 30 Carbine, over a full house charge of Blue Dot powders - and here I go tellin' ya 'bout the importance of bore to bullet fit (LOL).
But also, the 30 Luger, being a jacketed bullet from the start, was designed for military purposes and smokeless powders. The groove depth will most likely coincide with that application and not be deeper than .002, which makes me wonder if a plain based cast bullet will give you superior accuracy over a gas check, which can be driven at factory velocities so ya'll don't have to go cutting recoil springs to get those toggle tops to function.
Right off the top of my flat little head I do not recall the bore diameter of the 32-20, or the 32 S&W spls or 32 H&R, but there are some nice looking swcs that I have wondered about for general overall plinkin' and bunny bustin' with the 30 Luger. And, as I am absolutely certain you already know, if there is a gas checked capable bullet out there, the gas checks used for 308 bullets will certainly suffice for a .310-.311 bore.
BTW, I understand that the maker of magic cartridges, J.D.Jones, has designed a 7.63 Jones or whatever, using the 30 Luger case and a heavy bullet - he did the same with the 7.62x25mm and calls it the 7.62 JD or sumtin or anudder. Possibly he may be s source of information for you.
Otherwise, I would go cruisin through a bunch of older Lyman manuals that may have pictures of cast bullets to help you with ideas. HTH. Mikey.