My department has a similar policy regarding modifications to firearms. One of the few exceptions is that we do allow our people to change their sights. When we first started our optic program we allowed the user to mount their optic, or they could bring it to us on the first day of class and we mounted the optic for them.
By that time we'd been using 36 optics among the various subgroups of the weapons training unit with round counts ranging from a few hundred to almost 40,000. We only had two optics come loose, and we didn't know what we didn't know.
Once we started to see the trends in mounting failures as more and more people started coming through the class (it's a 1,000 - 1,200 round class so if there's a problem we often see it during the class - but not always) we started looking into best practices. There had already been several discussions here on PF and after talking to several people including @
Wayne Dobbs, consulting with a mechanical engineer, and experimenting with different methods and products, we came to what we think is a good mounting procedure to minimize problems. The procedure has been revised a couple times, once specifically because of input from a member of this forum who suggested test-fitting the screws and plates and such to make sure everything fits before going too far in the process.
We tracked information about the implementation of the program last year, sent surveys to participants, tracked scores during the class and on a mandated later date, and did a bunch of research, testing, and experimentation. We tested aftermarket screws from McMaster-Carr (and are still testing stainless steel versions) and found them to be at least as good if not better than those provided by most manufacturers. This testing involved firing 10,000 rounds through a pistol with an optic mounted with the screws, corrosion testing, and various other procedures that I won't bore you with.
All that to say we learned from our mistakes and the experiences of the participants in the program and narrowed most mounting failures to failure of the thread-locker. This included not using any threadlocker, using products that suck, not putting the threadlocker where it needed to be, using too much (especially in the case of Vibratite VC-3), not allowing it to cure, and not removing oil, solvent, or grease from the interacting components prior to assembly.
When it comes to optics we don't have the compressive force as if we were driving a screw into two pieces of wood, and we're not using the torque we would when putting on wheel lugs, so in order for things to stay where they should under the violent reciprocation of the pistol's slide, everything needs to stay in place. This is one reason I don’t like plastic plates. I believe that they have a higher potential for movement between the optic and slide which can cause the screws to vibrate loose.
We had the procedure largely formed about three months into the program and sent out an email to all optic participants letting them know the proper procedure. We also started encouraging people to not mount their own optic prior to the class.
Early this year we started mandating that all optics be installed by our armorers at least 24 hours prior to the class to ensure they are mounted properly and to allow inspection of the pistol to ensure it complies with policy. We recommend they wait 24 hours prior to zeroing in order to allow the threadlocker to cure, but sometimes that isn’t practical, so we’ll have them zero immediately after installing and then we’ll re-check the torque once they’ve zeroed. We’ve had very few optics come loose since.
Optic Mounting Steps:
- Inspect pistol to ensure it is compliant with policy and has backup iron sights
- Inspect the optic to ensure it is an authorized model and is functional
- Test fit the optic, plate (if applicable) and screws to ensure they are compatible
- Degrease all interacting parts (slide/plate threads, screws, excess oil in optic cut or on plate)
- Apply Loctite 248 to the screw threads where they will engage with the plate and or slide threads
- Tighten the screws until resistance is felt then apply alternating torque until the specified torque spec is reached
- Apply indicator marks (I prefer oil-based paint pens – put the paint on something and then apply with a toothpick unless you really like taking risks)
- Co-witness the reticle to the backup iron sights to make zeroing easier