It's funny how the rifle gods work. After a recent discussion on the forum concerning Hopkins & Allen rifles I fell into one this morning at my local dealer that he had just taken in. After closely examining it I knew that I was going to walk out the door with it and so I didn't really haggle over the price. It's a medium frame in 38 centerfire [38 S&W]  with a bright shiny bore, decent case hardening and 90% + wood and bluing. The bore slugs out at .359 and the chamber is clean and snug. I'm wondering if anyone can give me some tips on loading for it. I just ordered a set of dies and I've got some brass left over from a Police Positive that I owned many years ago and a Lyman 158 grain semi-wadcutter mould that I got somewhere but never used. When I get it right I'll probably be shooting this rifle a lot. These rifles are great for walking around with, shooting steel with at 50 yards and tipping over the far to common feral cat. In the meantime baby's got a new home and we're going to have some fun.

I think you will be OK with most any load published in a reputable manual. If you are concerned, use the starting loads. 38 S&W was not typically loaded to high pressures due to the many cheap revolvers of the old days and I think modern loading data reflects that.

Hopefully your Lyman mold will drop bullets that will be a proper fit to the barrel. It should be okay, but no way of really telling until you start casting.

If your bullets end up being a trifle undersized, start looking for molds intended for the .38 S&W cartridge, which uses a .361 slug. All of my molds were obtained from NOE, and will drop at .363 and .364

I imagine the majority of folks reloading for that round are content with using bullets or molds that actually intended for the .38 Special family of cartridges, and given the condition of many older revolvers, that is probably just as well. 

I’m sure you are aware of all this, but I’ve had more than one mold from Lyman that cast undersized or oversized from what I was expecting!

       The rifle is definitely a 38 S&W. Just loaded 50 rounds with 21/2 grains of red dot and bullets from 125grn .356 dia. up to 158grn .358 dia. The .358 bullets engrave so I'll see how it goes. I haven't disassembled the rifle to check the breechblock link because the rifle is too nice to lay a tool on.