Daryl's right. Some are reported to be long. Be careful!

I have had good experience using a Lee .377 {for .38-56, .38-56, not .38-55} expander in a Lee 7.5x55 die {what I had laying around} for 9.3x62 brass made from Win .30-06 cases and I suspect same will work for x57 if need be.

BTW: The case is run over the expander only and is not allowed to enter the neck/shoulder portion of the 7.5 die. I have gotten hard crush-fitting with this method and have had no need to go beyond .377.

Both my 46 and 146 have chambers that do not need such expansion. Remington and Prvi 8x57 cases expand fine in the Hornady die and headspace A-OK in my rifles. The Prvi case necks are thicker than the Remingtons I've expanded.