9mm does not make major. the weight of the bullet x the speed needs to be over 165,000. the only way you can make it with 9mm is to fill it with a lot of powder. Also the 9mm doesn't generate enough gas and pressure to really work a comp
If you use a 125gr bullet, you don't need to push the bullet as fast as a 115, but if you go up to a 147, then you don't have enough gas.
Ohh okay, I get it now, thank you!