Rocky - They do have 2 guns available; one for single player and an add-on gun for 2 players. The 2plyr gun is different in that the control box says 2-player and the switch on the side has 3 positions for 1 player, 2 player, & calibration.
The gun I have is a couple years old and is the ray gun style. As mentioned above that this works with the 2nd player gun.
The difference between the two guns (player one and the add-on for 2 players) is this switch.
First, it is important to know that ActLabs guns emulate a four buttons mouse.
The normal PC USB gun has a two position swith (Calibration and player1). When you wanted to calibrate, you swithed to calibration position. After that, you switched to 1 player position. In this position, the gun works like a two buttons mouse, where the first button of the mouse (button1) is the trigger and the second one (button2) is the reload button. There is no option to use the button3 and button4 of the mouse (built in hardware) driver.
The new PC USB gun (it works for one or two player, not only for two player), is like the old TV USB gun about the switch. It has three positions (calibration, player1 and player2). The first and second is the same like normal PC USB. The third position (player2) redirect the trigger press to the button3 and reload button press to button4 of the mouse driver.
So, before Mame104u5, if you want to play two players gun games, you must have one of the gun with the switch in player1 position and the other in player2 position, and remap player2 control to use the button3 and button4 for the second one. Mame do it for you when use -dual_lightgun option.
But after Mame104u5, with the new raw mouse driver included in Mame, you don't need to use the dual_lightgun option, because each gun is managed separately. You can use two actlabs gun in the player1 position.
I hope this help you.