The rest of the gun doesn't matter. A two inch barrel leaves almost no space for the propellant to expand before it escapes containment (and all its remaining energy is wasted), and no chance for any useful rifling.
It's not just a 2 inch barrel though, it just starts with that, then has a plastic barrel.
Use metal for the start of the bullet where the stress is highest, then switch to plastic for the rest of it.
I agree the lack of rifling doesn't help, but what's wrong with a 2" barrel? There are snub-nosed revolvers with barrels just as short.