What you and Cpt. Virgil hilts forget is that muzzle velocity also affects the accuracy in combat. The faster the bullet, the less time the target has to get out of the way (which translates to better accuracy). I have my doubts the ammunition generally used at war is of "good quality", especially by the time it finds it's way into the barrel.
I'm not saying Thompson was a bad weapon (actually rated it as third in my preferrences), but it isn't the holy grail of SMG's either. It did have some considerable shortfalls, which of the weight was most concerning. And if anyone noticed, I didn't give much praise to MP40 or Sten either (let alone the japs).
Accuracy is accuracy. Muzzle velocity affecting accuracy in combat is a crock of crap. Velocity only affects the amount of lead necessary to hit a moving target. And if you are shooting at humans moving at a range at which a pistol round is effective, 300 feet per second is not going to affect lead enough to bother with. It won't affect bullet drop that much inside the effective range for a pistol round, either. A 45ACP 230 grain slug will cover 100 feet in less than 1/8 of a second, (and a standard NATO 9MM round covers the same distance in just under 1/10 of a second) exactly how fast do you think a human can move? You're talking about the difference between leading a target 5" vs. leading it 6", and even less difference than that in bullet drop. In combat, an 8" group is considered excellent, and you're claiming a maximum difference of 1" lead (if that) is an accuracy advantage?
And 100 feet is about as far as you fire an SMG, more distance than that and you use a rifle or a SAW. You just do not engage at much over 1/3 a football field with an SMG. And if you do, 300 feet per second in muzzle velocity won't make a real difference either. Yes, you CAN hit a person at well over 100 feet with an SMG, a decent marksman can do it at near twice that distance, if he's had practice. An SMG (as well as a pistol, for that matter) is a CQB weapon, for use at hand to hand distance up to about 100 feet maximum, most often from hand to hand up to 50 feet or so. If you're engaging the enemy at a distance greater than 100 feet with a pistol round, you've got a lot bigger problems than the choice some guy made about the round you're using.
All you are doing is foolishly confusing marksmanship with accuracy. It is not the same thing. There are three "advantages" 9MM holds over 45ACP in military use. One, less recoil, two, lighter weight per round, and three, NATO standardization. It is NOT more accurate. In fact, given a 1911 Colt in 45ACP and an M92 Beretta in 9MM, both drawn from the same armorer, the 1911 will out shoot the M92 at least 8 times out of 10. Get into the Spec OPs issue weapons and most often the 1911 shoots at least as well as the P220 in 45ACP, and both of them will most often out shoot the P226 9MM.
Decent 45ACP 230 grain ball ammo is pretty much the same. Like I said, my P14-45 functions with the cheap stuff rather well, and shoots a serviceable group with no problems. And military grade is BETTER than the cheap white box junk from the five and dime store. I know this for a fact, because I get access to military 45ACP, the genuine article, exactly like an U.S. military member gets issued in the field. It shoots better, and cleaner than white box Winchester you buy at the store. I shot a brick of each last fall, and the military ammunition shot tighter groups, was 100% reliable, and left my weapon far cleaner.
