Can you fire 9mm in a hi point 380 acp?

Answer 1

Noop.

A 380 has a 9mm projectile, BUT, the typical 9mm Parabellum, or 9mm Luger have longer cases and develop much higher pressures.

A 9mm will not chamber like a 380 (in a weapon designed for a 380), the case will stick out about 2mm. In most pistols, this would prevent firing. In other pistols, the gun may still fire.

Now High Point pistols use BLOW BACK as their auto cycling system. This means that the recoil spring and the slide present enough resistance & inertia for the rearward force, to allow the projectile to leave the barrel before the case is ejected. These are BALANCED for a low-powered 380 ACP round.

Even if one could get the gun to fire with a 9mm Parabellum, the fact that 2mm of the case is unsupported, AND there will be 2-3 times the energy involved means there's a high likelihood of the gun having a catastrophic malfunction. The brass case will likely rupture and the slide will likely derail and be thrown backwards (towards the shooter's face).

Even IF one could fire successfully a few times, each time would weaken the barrel, the slide and the recoil spring. Which means the pistol could kaboom (blow up) any time, maybe after the 1st round, maybe after the 30th round.

Use the right ammunition for the gun and you will have nothing to worry about.