I would add a couple of points. One, get Starline long 38-55 brass. It is likely the only available case that will properly fit your chamber. Two, as mentioned the groove diameter of 38-55 barrels can run well over .380" Most of the time if a bullet big enough to fill the grooves is seated in a case, even the thin Starline ones, the round won't chamber. This is because the chambers are dimensioned for use with black powder. A soft lead bullet loaded over black powder doesn't care if it is a few thou under groove diameter. When the powder lights off it will fit properly, and shoot accurately. Trying to fire a hard lead bullet under groove diameter over smokeless powder will lead to gas cutting, leading, and poor accuracy. This is why so many people have trouble getting their 38-55s to shoot well, they don't understand how the gun's dimensions relate to each other and to the cartridges and they insist on using modern loading techniques and propellants. Make ammunition for it that it is designed to use and it will perform very well. Feed it something it's not designed for and it will not work right.