Fitment issues on picatinny rails - Warne Red-Dot Low Profile Reflex Mount

I bought this to use on a Ruger PC Carbine, but it wont tighten down enough to grip the rail, resulting in the mount shaking around significantly (about 1/8" of play). I tried to use it on a few other picatinny rails I have and of the 4 I tried it only snugged down on one. The customer service from Warne and Optics Planet was excellent, but at the end of the day this product doesn't work for the firearm I intended it for.

An additional issue I had is that the optic I intended to mount on this (Primary Arms GLX RS-15) did not have screws that worked with the C-More footprint this mount accommodates. Not necessarily the fault of the mount, but it only comes with 2 screws, so if they aren't what you need and your optic doesn't have the right ones you may have difficulties.