Barska 4x32 - Barska 4x32 AR15 Waterproof Rifle Scope, Mil-Dot Reticle

I mounted the barska 4x32 on my smith & Wesson m&p 15. The scope looks great mounted on the gun but I had to re-tighten the screws after every 30 rounds. When looking down the scope it also had a bubble in the bottom corner which I assume is a factory defect. I waisted 90 rounds trying to sight in my rifle because I could not get it to stay tight. I'm my opinion it is a complete piece of garbage.