Dave,
If you are going to try lead bullets I would suggest you first make an impact casting of your chamber throat. Fill a case with lead and then push a lead plug down the bore onto the lead filled case. Using a piece of drill rod that fits as close as reasonably possible upset the lead plug. When you withdraw the case you will have to push out the lead plug (into the chamber). This will give you a good idea of the throat length and diameter.
If you fill the throat gas will not escape past the bullet as it enters the bore.
A cerrosafe casting will also provide the same measurements
I suggest that you use a little softer alloy rather than a �hard cast� bullet. The vast majority of the bullets I cast and shoot are less than 20 bhn. I prefer bullets with a hardness of between 12 and 14 bhn for hunting critters of deer size and smaller.
You may want to check with Marshal Stanton at Beartooth bullets. Marshal offers bullets heat-treated to 22 bhn or on special order he will furnish bullets at 18 bhn. I believe if you try both bullets you will find it easier to develop accurate hunting loads with the softer bullets. If you fill the throat you will not have problems with leading.
Marshall can provide special sizing diameters and he is familiar with the Marlin rifles chambered for the .38-55 cartridge.
You will not find a better cast bullet than Veral Smith�s LBT style bullets but if you prefer to cast your own and want to get started for the least money you will do well to start with the Lee 255 grain bevel base bullet mold. The mold is low cost and the bullet seems to shoot very well in both my .375 Winchester and my Fathers .38-55 Encore. We shoot them as cast with tumble lube and hand lubed using Javalina 50/50 Alox.
You will have no trouble shooting cast bullets at full power in the .38-55.
