would like to mount an x300 flashlight to it for a carry gun... But I am worried that it will cause problems
It shouldn't cause problems with the function of the gun, or at least not with a metal framed one. Can't say about the poly guns, they seem to have different rules.
What bothers me, and where I think you are setting up for potential problems is mounting the light on your pistol. I realize "everyone" is doing it these days,and the guns come made to do that, I just think its a poor idea, particularly for someone who does not carry the gun professionally.
And even the professionals, who get, and are required to pass training don't always follow it. Just look at the news.
TO me, its in the same class of dangerous foolishness as using a scoped rifle instead of binoculars. You are pointing a loaded gun at what you are
looking at.
Everyone says "I'd never do that"...and of course, we're all completely safe all the time, but I think, if you're human, and not rigorously trained (and perhaps even if you are) at some point you are going to do it.
Its all good, until someone gets "accidentally" shot, and maybe killed...
Also, consider the legal aspects, if you're not a cop, shining a light attached to a gun on someone IS pointing a gun at them (don't care what you SAY) and that can be a legal threat, can be a level of assault, or brandishing and leave you open to charges.
Assuming you don't run across one of the folks (some of whom are cops) that figure someone pointing a gun at them is a deadly threat and they shoot you!
I've heard all the arguments, I know the pros and cons, and I think a light NOT on the gun is ok, and a very good idea, but a light ON the gun is a risk and a problem in waiting. MAYBE it never happens to you, hopefully not. But, if it ever does, who is really at fault? I'd say its the guy with the light on his gun.
Just my opinion, and worth what you paid for it,