In my two .38-55s I had my best luck with the RCBS 250-grain bullet, usually with the gas check. Powders which gave me the best accuracy in the 1000-1200 fps range were Unique, IMR4227, and RedDot. Higher power loads used RL7. According to current Lyman data, RL7 gives the highest velocities with the lowest pressures. Check the bore diameter, many .38-55s have bores approaching 0.380"; choose/size your bullets accordingly.