I have seen several post with pics of 9mm ARs with rails. I attempted to mount a KAC on my Colt, but there was nothing to secure it to (Gas tube). How are you mounting the rails. Mine is fine until you put pressure on the VFG, and then it twist. Sorry if this has already been discussed.
Thanks
i have a YHM free float rail on my 9mm … it works perfect. No movement at all.
I believe the reason why yours is twisting a little bit is because you might have a 2 piece hand rail which needs to be attached to something at the end towards the barrel.
The VFG (vertical forward grip) actually amplifies the looseness of having a 2 piece handrail. Kinda of think of it as like a … tire iron… the longer the handle is, the easier it is to torque (does that make sense?)
I hope this helps?? 
Here’s mine
norman
The KAC rail needs to attach to the hand guard cap at the front sight base and then tighten the screw on the top rear, which it seems you have already done.
I ran a DD rail on the last one I used.
Stickman,
thats a nice piece of machinery you have there. 
I need to get some photo equipment like yours!
Bondster, have we helped you with your questions?
Get a RIS with the UK lower rail and it will lock in just fine.
What rail do you have?
It’s a two piece that uses the delta ring and endcap I assume? Good 2-piece handguards ought to have nubs that fit into a couple of the notches in the barrel nut. That and the gas tube usually keep them in place.