ALTERNATIVELY, restat the SMG to a .45 ACP (11.43x23mm), which tears unarmored targets a new asshole closerange, minor bruising (if that) at longer range. I have suggested in the doc to turn the SMG into a .45 ACP, and lowering the magazine size to 25 as opposed to 45.
If larger calibre was better, we'd still be at .75 caliber flintlock muskets.
The .45 may have been great in cowboy and gangster times but it's pretty obsolete in anything with full auto; it's more of a mark of the Americans' unholy love affair with it and of their industrial base more than for real merits. Note that for everyone else, on both sides of the iron curtain, the 9×19mm was considered good enough and eventually overkill.
More recently even, the FN P90's 5.7×28mm has greater range, accuracy, and terminal performance than the older 9×19mm standard and is capable of penetrating body armor.
A retired Airfield Defense Guard (Classified as counter-special-forces) told me that a P90 is fantastic at point-blank, but terrible at range. To paraphrase: "If you shot me in the head point-blank with something like the FN P90, I'd be dead. If you shot me at three-hundred meters with the same gun, I'd have a small bruise on my forehead."
Same goes for the 9x19mm, although good luck hitting anything over 50 meters. The 9mm is actually greater calibre than the 7.62 of something like the AK47, however, the AK works at range because of the smaller calibre and higher power cartridge. The 9mm isn't even much of a step-down from the .45. It's 9mm compared to 11.43mm in calibre and 19mm compared to 23mm in cartridge.
As a general rule, the higher the calibre, the faster it bleeds off energy; the longer the cartridge, the farther it will fly; the combination of the round's speed at time of impact and calibre is the damage done. Hence why long range .50 cal rounds have such a long cartridge, because they need the power to give them range.
The energy of a bullet is given by F=ma. The mass of a NATO 9x19mm para round between 7.5 and 9.5 grams. The mass of a typical .45 round is 12-15 grams. Assuming high-end on both [low-end will be done in sq brackets], 9.5g and 15g, both have a muzzle velocity of 300 m/s [7.5g 9mm 410m/s; 12g .45 373m/s]. Just looking at these we know the .45 is gonna fuck you up worse at point blank.
9mm Force in Newtons = 0.0095kg x -300 (300 m/s/s deceleration as it hits your skull and presumably stops) = 2.85 Newtons of force concentrated in the point of the bullet.
.45 Force in Newtons = 0.0150 x -300 = (you're not gonna believe this) = 4.5 Newtons. That is nearly double point-blank force for a mere 2.43mm more diameter and 4mm longer cartridge.
I can't be arsed to find out the velocities of the bullets at range, but a .45 bleeds the speed off a lot quicker and 9mm is more effective than .45 over range.
A 4.43x33mm round has no place in the 25th century, or even today. If you have an assault rifle which kills for 700 meters (pulled out of my ass here, it's 1:00) vs an assault rifle which kills for 1300 meters but doesn't guarantee a kill with each like the former could, then there's no competition. If you're only expecting to fight within 500 meters then there is absolutely zero reason to take the latter of the ass-pulled imaginary hypothetical rifles.