Below are my railed guns: From left to right: G19 - G20 - HK45 - HK45 USP Tactical From left to right: G19 - G20 - HK45 USP Tactical - HK45 (pls.- don't ask why I switched the order). I'd like to rotate the X300 between these 4 guns. Surefire says the X300 "Fits picatinny or universal rails", but as you can see each gun sports a completely different rail profile. That's where I'm getting confused. "Picatinny or Universal" denotes two different rail types, yet...as you can see...pictured above are four different ones. Also, out of the four, which ones are the universal and pictinny? And what are the other two called? If I'm going to need an adapter could you please point out which one. I'd like to get my online order in today, so if someone could please clarify it would be much appreciated. Thanks. ETA: Please feel free to recommend other accessories, i.e., dual switch, grip switch, etc., that you feel adds considerable valuable advantage when coupled with the X300.