Originally Posted by DWalt

The Starline 9mm SuperComp case has the same head/rim diameter as the 9x19mm. It is not of the semi-rim style of the .38 Super case, but it is otherwise identical and will work fine in any .38 Super pistol having a chamber cut to headspace on the case mouth. I once talked to a Starline engineer and he said that the SuperComp case is very strong and will withstand high pressures of very hot .38 Super loads. I have used them to handload 125 FMJ bullet loads having an MV upwards of 1400 ft/sec. I would recommend you use the Starline 9mm SuperComp case instead of .38 Super. I've had no problems in using them in either of my two .38 Super pistols (Colt GM and EAA Witness). They also work for use in 9mm Steyr or 9mm Largo pistols.