It seems to be a rarity on a S&W,,there are a few other brands that have problem screws that back out regularly.
If a screw keeps backing out when the gun is used,,even though the screw was torqued down to spec before hand,,then something has to be done.
One way ,,,You can walk around with a small screw driver in your pocket and continually look at the screw and hope it's still there. Checking and tightening that problem screw every time you think of it and then some.
One reason the screw keeps loosening even when tightened down correctly is that the threads on the screw or in the frame (or both) are loose spec. Easier said,,a poor fit.
Parts that flex during firing like the side plate add to the loosening effort and these can become undone easier than others on some guns.
Shotguns and some rifles with large side plate covers on the frames are subject to loosening from flexing while being shot. The Marlin hammerless pumps are bad for this. They added lockscrews to the second generation of them in attempts to solve the loosening.
Anyway,,
A second method to tighten the fit is to 'crush' the screw in OAL,,the threaded portion actually.
It's done simply by eye and feel and a hammer on a lead block.
A couple careful wacks to the threaded end of the screw to compress the threaded shank will take up the TPI by a .000 or 2. That will improve the fit of the screw threads to the frame threads.
No more sloopy thread fit.
Don't go too far as the thread on the screw will be too far compressed and will be out of the TPI spec of the frame and won;t thread back in. Out of luck now,,time for a new screw,,
It also works to retime screw (draw up) for bringing screw slots to the 12 to 6 position on high grade guns. You can gain about a 1/4 turn this way but you can also ruin the screw if you over 'adjust'.
Touchy work,,yes, But I do this all the time .Customers love 'timed' screws on their high grade and even low grade guns.
The third method is to get the blue loctite out. Carefully clean the screw and the frame threads.
Apply the minimum amt necessary w/a toothpick and tighten the screw home. When cured,,it'll stay put during any normal service. You can leave the screwdriver at home and not worry about looking to see if 'that' screw is still in the frame or not.
The thread locker is just taking up the poor fit between the threads in the frame and the screw that already exist.
If you need to you can easily remove it with a screwdriver and normal torque with the correct Locktite .
With all that said,,it's a rarity that Locktite has to be used. I would not use it on screws on a gun as a normal re-assembly routine just to 'make sure' they didn't back out.