Guns like Thompsons, MP5, MP40 are called “sub-machine gun” in English-speaking countries. However, they are called “machine pistol” in many European languages, such as German.
So which one is better? SMG do fire pistol rounds, instead of rifle rounds, which is argubly the most definitive and distinctive feature of SMG, so in this sense machine pistol seem a better name.
In addition, SMGs are rarely used like a MG. MG are mainly for suppressive fire and fire support, SMGs, though called “sub” machine guns, are used for very close quarter combat, and almost never take the role of MGs in that their penetrative power and duration of fire (they generally get only 30 rounds) as well as accuracy and range are incomparable to that of MGs.
In short, it seems to me machine pistols is a better name. SMGs seem nothing but a pistol that can fire rapidly and share many drawbacks as well as advantages with pistols, e.g. light-weight, inaccurate in long distance, lower stopping-power, both uses pistol rounds instead of rifle rounds, lower recoil, used for close-quarter combat, etc.
My distinction is that a rifle is fired using both arms and a pistol is fired using one (usually).
The rate of fire is not an issue given this distinction.
But I could be wrong.
ETA: You want ‘submachine’ not ‘sub-marine’ in the poll.
Pistol is a form factor, not a description of what round a firearm fires. You could build a pistol that fired .30-06, and it would still be a pistol. You could build a rifle that fires .357 Magnum and it would still be a rifle not a pistol.
My understanding is that Personal Defense Weapons fire a bullet which is closer in performance to a small assault rifle round than to a pistol round. It’s intended to have penetration sufficient to challenge body armor and to have longer range than typical submachine gun/machine pistol rounds.
To my way of thinking, the term “Machine Pistol” ought to be reserved to ultra-light weapons like the Beretta 93R, Calling the classic Tommy gun a “pistol” is a bit of a stretch.
Another reason I’ll go with “sub-machine gun”: to anyone with any experience with military rifles, like the M-16 or AK, firing an MP5 or an Uzi with the stock extended is basically a familiar experience. The range, accuracy and recoil characteristics may differ, but the muscle memory is the same - raise to shoulder, aim, fire; whereas someone whose only experience is with pistols will have a much harder time. Therefore, they are much closer to full-sized guns in terms of usage than they are to pistols, which makes the term “machine pistol” inappropriate.
PDW is kind of an industry term. At least one, the PP-2000, shoots plain old 9mm, although overpressured. The newly designed rounds are designed to have greater AP capabilities than a regular pistol, although they certainly are nowhere near rifle calibers in kinetic energy or “stopping power.” The 5.7x28mm is probably the best well known, and not without controversy (“It goes right through armor! Cop killer bullet!”)
They do make rifles in .357, .44 etc. They are almost always lever actions with tubular magazines. Marlin and Henry make a bunch. I have no idea how a pistol round affects ballistics. Also, I think they are generally called carbines, but I’m not sure if the length is because longer is worse or just because. There are also semiautomatic pistol round carbines, like the Beretta Cx4 Storm or Hi-Points.
As I understand it, a Carbine is just a short rifle. Compare the M-16 Assault Rifle to the M-4 Carbine, which is essentially an M-16 with a shorter barrel and a collapsable stock. The two weapons are effectively identical in every way that matters aside from that.
Both are bad names. I’d prefer Sub-Assault Carbine or Automatic Carbine as the term for what we currently call SMGs. SMG itself is a contradiction of terms and machine pistol fails to accommodate the usual stock, extended magazine and two-handed use that the term needs to communicate.
