Sightmark reflex sight - Sightmark Sure Shot Reflex Sight

I like this sight, mounted on a Ruger MarkIII 45/22. Was pretty easy to sight in, seems to hold zero. I don't like that the description said this unit had a locking screw, but mine does not. My sight is obviously different than the one pictured on the directions.
That said, the different reticles are sharp, easy to see even in daylight. This one, like every oter red dot sight I have began getting dimmer during shooting. I put a thin piece of cereal box cardboard on top of the battery, like my other red dots, to cure this problem. The range I use has a dedicated .22 range with swingers, gongs, dueling trees, etc. I might go through 500 rounds in a shooting session, and this sight is holding up.