>>279777088Vigilante high schooler Deku is not obtaining a gun. Guns have been shown to be very rare outside the government and usually need connections to organized crime to obtain them illicitly. There's really not that much he can use to overcome the physical and technical disparity between him and the villains unless he just ambushes the smallest time villains, basically women with bad quirks and schoolkids, with a pipe and wires.
He could still age up and become a cop as All Might suggested, but the cops suck and I don't think we've ever seen the cops take down a villain without the help of pro heroes.