In Area 51 and Maximum Force, you have to shoot the very edge of the screen to reload. The Act-Labs gun simulates a right mouse button press when shooting off screen. I am going to ask the Ultimate Patchers if they can create a "cheat" that will move the pointer to the far left an simulate the trigger; if this could be mapped to the right mouse button, those two games would play properly.
Until then, there is an unlimited ammo cheat for Area 51, and probably one for Maximum Force.
Other gun games such as Sharpshooter and Police Trainer don't require shooting offscreen, and thus don't have those problems.
There is a minor issue for games like Operation Wolf that use more than one gun button. There is a side button on the Act-Labs gun (again, the right mouse button), but it doesn't move the pointer. To use this as a grenage in Operation Wolf, you first have to shoot the target with the regular trigger, and then quickly press the second button.
Finally, the trigger only shoots once, no matter how long you hold it down. Maximum Force has a machine gun as a powerup, but you have to pull the trigger for each round; same in Operation Wolf. I wish the gun had a switch for an "automatic" mode...
Other than these quibbles, I'm happy with the gun... I can play Sharpshooter for hours...
--Chris