would this fit on a 10.5 barrel 223 pistol with a quad rail. I believe there is 9 slots on a 10.5" — 1 Answer

It is 7 1/4" long in total so you'd probably want to have a bit extra room unless you want to open both pins each time you take it apart. 9 pic rail slots is the minimum amount required to hold the screws. With two 5 slot pic rail mounts on an mlok, it still has overhang on the front and back. If you have at least a 7.5-9" rail, you should be all set. 10" is a good length rail for it. Any would work fine as long as it's 7.5" or more. But 7.5 is going to be right up against the magwell, making it so you can't open it up by only opening the rear pin. Sorry you had to wait so long for a reply. Hope you got one and it worked out for you.