Originally Posted by
SoCalDep
The torque you are using is very excessive. Those McMaster screws are great for RMRs and SROs but the diameter of the head is too large for Holosun 407/507/508 series optics. When mounting, the edge of the head contacts the side of the optic body prior to the screw seating fully in the optic pocket.
With the aluminum frame models, the harder steel screw is able to slightly deform the metal in the optic body, allowing it to seat (maybe), but the 508T, being made of titanium does not deform and causes the “misperception” that the screw is seated when in fact it is being held with minimal contact between the edge of the screw head and the optic body. Upon firing the pistol, the screw and/or optic body is deformed during the significant reciprocating forces of recoil and once that minimal interaction is compromised the optic almost instantly becomes very loose.
If one looks at engineering specs for torque on various fasteners (screws) based on size and material, they will see that the specs listed by optic, pistol, and accessory manufacturers already commonly exceed generally recommended specs. Adding another 50%-100% is not something I’d advise and it’s tantamount to treating a sunburn with Windex. It’s unlikely to solve the problem and there’s a good chance it will make it worse…. The scary thing in this case is that the worse may just be a bit further down the road.
Because we’re attaching two relatively non-compressive materials, the torque provides minimal assistance with preventing the optic from coming loose, assuming that they are seated and “tight” to begin with. Keeping the screws from coming loose is a combination of threadlocker and preventing movement of the optic relative to the screws.
When excessive torque is applied there are a number of potential outcomes, but in the case of optic mounting none are good. Best case is that the torque does not exceed the yield strength of the material, remaining in the range of elastic deformation. In this case, the torsional forces applied during mounting dissipate rapidly, but since the materials being joined don’t compress you get minimal benefit.
If the yield strength is exceeded then the screw’s strength is compromised and the extra money you spent on those alloy steel screws is wasted.