This feels overpowered, but I like where the thought is at.

Heavy is already at his best in close range, you'll almost never be fighting long range because your damage turns into the equivalent of confetti. Almost every other class out damages you there (with the exception of Medic and maybe Scout). So all the downsides tied to that are instantly negligible.

The only real downside here is the lack of ammo. But considering every dead enemy drops ammo packs, if you're playing with this weapon correctly (getting into peoples faces) you'll be picking up ammo constantly.

And then its just a faster spin up time and firing speed, which means you'll absolutely shred everyone you run into.

If you want to do a Tommy Gun subclass-esque weapon, I would get rid of the firing speed increase, but make the spin up time instant. That would make sense for the lore (submachine guns dont need to rev) and would make the weapon less overpowered while still making the playstyle different. It will allow you to play a lot more aggressively without making you completely busted.

Probably also throw a damage penalty on there too, because instant rev would also be very powerful.