I use a .40 cal, store bought, 42" length, and made of aluminum.
My ammo is: Sharp wire darts, spear point darts, stun darts, and spike darts.
I use the sharp wire darts for target practice. My target is a cardboard box filled with plastic shopping bags. I tape a 50 yard small bore rifle target to one side. I can put a dozen darts in a 2" circle from 20' without trying. Once I put a dart directly on the top of another dart!
My stun darts are all plastic. I use them to train the cats and dogs where not to go in the house. My dogs quickly learned to stay away from the garbage and there have been no cats on my counters since I started this method.