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Let me add one variable to this equation..
My rifle has 45 degree offset BUIS at the one o'clock position. I need to mount my Protac RM 2 and I will use the pressure switch. I would prefer it on the right side - but my BUIS are in the way. That leaves me ten o'clock or what about on the bottom? say around five o'clock. What are the cons with a light mounted below the barrel. Is shadowing that bad?
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How far forward of the rail is your muzzle? I have a 9" barrel (add on BCM Mod 1 Comp) with a 8" rail and so my light pretty much sits at muzzle length (a reason why I also put a clear cover over it) so my shadow is minuscule. If it was say a 7" rail on 16" barrel the shadow would be worse, but could it still be useful? That is up to you. The thing about mounting lights on the sides is not a cover blocking light issue, as you can just lean/compensate more for it, but more of if you have it mounted on the left (for example) and on a left barricade you expose more of yourself than if it was mounted on the other side. That is why some have taken up mounting a pistol type on the 12 o'clock in front of the front sight.
Frankly, we can tell you all day long what works, and then find a situation where it won't. Your best bet is mount it, try it, adjust until "it feels right" for you.