What Advantages Do Submachine Guns Have Over Personal Defense Weapons

Are there any advantages that sub-machine guns have over personal defence weapons?

First lets look at your Terms, as there seems to be some confusionSub-Machine gunGen 1 - ThompsonPersonal Defense Weapon Gen 1 - replacing pistols issuedLet’s jump forward several generationsSub-machine guns are pistol caliber by definition with fully automatic firePersonal Defense Weapon - can be either self-loading only or fully automaticCan be Pistol Caliber but may be more powerful caliber, so there is a cross-0ver in that the SMG can be a PDW and a PDW can be a SMG.The Idea of the SMG is that you had at the time - Larger Magazines than issue rifles and ability to shoot many more rounds quicker than an issue rifle. This carried forward to WW2 with MP40’s, PPSH’s and M3’s being used in urban environments - This was upgraded to Sterlings, UZI and MP5’s - then the 9mm was found lacking because Ballistic Armor was being fielded by all militarizes.This developed into newer weapons using 5.56 NATO, 5.45x39,and 5.7x28 that can better defeat armor and issued as PDW like P90.Now one advantage that I see is that I can get magazines for olderSMG like UZI’s, STen’s etc for much cheaper than newer designs like the P90 or HK designs - and the price of 9mm ammo is much more reasonable than the price of 5.7 ammo - or even 223 ammo.Also aftermarket parts supply is much better for older SMG’s that were issued in large numbers.

What are the advantages and disadvantages that the sub-machine gun FN P90 has over most commonly used arms of its class?

Advantages:Ammo Capacity - The “standard-capacity” magazine of a P-90 is 50 rounds; the standard for most of its competitors is 25-30.Compact Size - The P90 fits this 50-round mag along the top of the receiver in a novel way compared to most other firearms, and coupled with its bullpup design it’s one of the smallest weapons available with its capabilities.Futuristic design - The P90 is iconic in its silhouette, guaranteed to turn heads at the range or on the street in a law officer’s hands.Disadvantages:Proprietary, Uncommon Ammunition - The 5.7x28mm cartridge was developed specifically for the FN P90 PDW and FN Five-seveN pistol. However, lacking the pedigree and widespread adoption of the 5.56mm NATO, 5.7 ammo was, for a long time, really expensive. Today, not so bad, but still about 10 cents a round more expensive than similar-quality .223/5.56 target rounds (about $26 vs $21 for 50 rounds of similar quality), and that adds up especially if you practice with it often. Nobody’s making inexpensive bulk paper-punching rounds in this size either, so going solely on the cheapest available stuff the price difference per round can double to 20 cents more for 5.7 vs bulk 5.56mm.Small Wound Channel - The P90 fires a round similar in size to the 5.56mm NATO, but with about half the powder charge and through a shorter barrel. As a result, muzzle energies of the P90 are less than half that of the 5.56mm NATO, and this significantly reduces terminal ballistic effects that make the 5.56mm more damaging than its size would indicate, and less incapacitating for about the same energy/recoil as 9mm or .45ACP.Weapon Cost - The FN P90 is the F’n P90, and FN knows it. The civilian PS90 (16″ barrel, semi-only) commonly sells for between $1000 and $2000 used depending on what was done to it, with the average “new in box” price being about $1400. Standard mil-spec AR variants sell as cheaply as $600 (less if you’re patient), with $1400 buying a small-shop custom build and $2000 representing an AR you can pretty much expect to take out of the box, zero up and hit the starting line for a 3-gun competition. For just over half the cost, you can buy a Beretta CX4 in 9mm Luger and have the same fun and basic capabilities in the civilian world, and save even more money on ammo (Winchester and Remington 9mm target loads are as cheap as a quarter a round).