The question of the security of non-pinned gas blocks has been brought up numerous times. Factory-pinned front sight blocks have taper pins, which secure the gas block/front sight assembly to the barrel. Aftermarket gas blocks in general come in clamp on, and set screwed types. This is because it is next to impossible for the end user to re-drill taper pin holes in a blank gas block to match ones already present on a barrel.
Since the Vltor VST-1C has provisions for a QD sling swivel, some people have brought up concerns that attaching a sling to the gas block might cause it to rotate, thereby rendering the weapon inoperable. I asked the guys at Vltor if they were willing to perform a test that would quantify the force needed to move/rotate one of their gas blocks and they were open to it. We decided on a torque test, which was measurable and relatively easy to setup. This would provide a number which some enterprising individual might use for further calculations (not me) if they wanted to.