I'm wondering, why hasn't anyone hacked a better looking gun, like a Saturn gun?
Howard C explained it to me, It's not that simple. There has to be a white pulse and some device to measure the time. The lightgun just picks up the white pulse. The PC gun was more than just a mouse hack to a light gun, it had it's own electronics to pick up the pulse and then translate the position as a mouse click. Mame treats the lightgun like a mouse.
Just hooking a lightgun up to a PC won't cut it. It needs that mouse ability and the device to pick the pulse.
When the button is pressed, the PC gun sent a signal to the box in the back and sent a white (all monitor guns on) to the screen. The lighgun optics picked up the white (because a monitor scans from left to right, up to down scanline) and knew the time and hertz of the monitor, then it moved the mouse cursor to that point. So it was kinda complex, like hacking an optical mouse.
That's why it's hard. Now if somebody can come up with a mouse PCB hack and the chips that ACT LABS used and fused them together to make such a system, yeah, you could take about any lightgun and hack it.