9mm is for all intents and purpose the same size bullet as the 38 spcl, .355 vs .357. The 38 spcl started as a black powder round and the 9mm started as a pistol round using smokeless powder at twice the pressure. It is pushing basically the same bullet faster than the 38 spcl and that is a plus. The 38 spcl revolver has a wider weight range and can shoot a wider range in bullet configurations so points to the 38 spcl. In my guns my 38s are more accurate than my 9mm so points to the 38. On the other had shooting at 100 yards I only have half the hold over with the 9mm so award points to the 9. I get more penetration shooting my hardball 9's than I do with my hardball 38's so points to the 9. Fact is you don't want me shooting at you with either but I will be using the 38 because it is more accurate and in my guns more reliable. My P94 has a bad habit of failing to eject all the time but my revolvers never fail to keep shooting, In my house that is a big point to 38.
38 spcl the maximum pressure for standard loads is 17,000PSI. Standard +P loading commonly around 20,000PSI. Common weights for the .38 Special round will vary from about 110 to 158 Grains. Length of a loaded cartridge is 1.55 inches.
9mm the maximum pressure for a standard load is 35,000PSI. Standard +P loading runs close to 38,500PSI. Common weights for the round 115 to 147 Grains. Length of a loaded cartridge is 1.169 inches.
Buffalo Bore Ammunition Ballistics
Round Type Weight Muzzle Energy ft/lbs. Muzzle Velocity ft/sec.
9mm +p FMJFN 124 465 1300
.38 +p LV JHP 125 306 1050
If I made a mistake that is on me, see your reloading manuals for more up to date data, I'm only speaking generalities and from my personal experience.