The SW760, or any semi auto clones of SMG's of this generation, are poor defensive weapons.
These weapons are poorly made, which translates into inferior accuracy and they are almost exclusively equipped with crude sights. This is of little consequence with an automatic SMG as they are capable of creating a pattern of bullets which cancels out poor accuracy with singular shots. Since the SW760 doesn't have a giggle switch, it has all of the handicaps of the original weapon, without the ability to spray bullets to compensate for inferior accuracy. The S&W 76 was a cheaply made, albeit reliable and effective SMG, its no suprise that a copy made by a fly-by-night outfit would suck. There are much better 9mm carbines to be had today, which is why the Navy has discarded the S&W 76 and other countires have discarded its contemporaries. I don't prefer the Kel Tec, though its a decent weapon.
I would reccomend a 9mm AR or Beretta Storm. I particularly like the Olympic 9mm AR which takes Glock magazines. 33 round G18 magazines are reliable, availible and affordible. Any other 9mm AR would also be an excellent choice, but the Olympic using G18 mags would be the best value. The Beretta Storm is also an excellent choice. Magazines are everywhere and reasonably priced and the weapon is reliable and accurate. The price is also very reasonable when compared to other 9mm carbines. I would also suggest a Vector Uzi. Uzi magazines are everywhere and affordible as are parts/kits. The weapon is extremely reliable and of all the SMG's of this
generation, its probably the best. Accuracy of a good Uzi carbine is quite acceptible. Even if you can get a SW760 that works, true S&W magazines are pricey*though there are ways around this*, the folding stock is flimsy and accuracy is abhorent. It would be fun to spray bullets everywhere, if you could get it running, but a Mac11 makes a better bullet hose..... My .02 would be to avoid the SW760 and the Kel Tec and buy a Oly 9mm. If you want a more traditional SMG, the Vector Uzi would be an excellent choice.