I haven't been able to get the offscreen reload to work, other than the method you described of quickly shoot sideways. I've come to the conclusion that this just doesn't work properly, and I'll be forced to press the B button to reload. However, for whatever reason some games (Lethal Enforcers for MAME) don't accept the button press as a reload. I have the button assigned in the Top Gun Control Panel, as well as enabling offscreen_reload in the MAME ini file, but no luck. Unless there is something else I can do, the only other option is to enable the unlimited ammo cheat for the games that do this. It's not ideal, but it's better than only having one round the entire game.