I went to the range yesterday to sight in my new scope. Got it down on the 50 yard range. Then I move down to the 100 and the damn thing came lose. Its way off after I tighten it. Then came lose again. Its as tight as one can get it without stripping it.

I have the A2 Upper Receiver, so I have a rail adaptor to hold the scope. The cheap ass scope I had on there first never came lose. Now I have the ANT 5x33 AR-15 Scope BDC For .223 with Rangefinder. It came lose at the adaptor and where it attaches to the rail.

The range master said to try fingernail polish remover to coat the screws with. He also said thats why everyone with military rifles has to start out on the 50 yd. targets because they all come lose.I thought about getting a bunch of small lock washers.
Does anyone else have a few remedies for this ?
My next upper will be a flat top.....

I always use loctite on ALL my optic mounting screws.

Most of those A2 rail/weaver mounts are very cheap.  Get a good one (ARMS) with a screw that has a rubber/nylon bushing in the screw, to hold it in place and keep it from backing off.  If it cant take a few rounds at the range, then it cant take a real life scenario.  With cheap stuff, sometimes you get real lucky, but you usually get what you pay for.  I have learned not to cut corners on optic mounting.  Each optic should be mounted as if your life might depend on it.  One day, it might.

Loc-Tite Blue.