I have the FastFire on my AMT Automag ll and it has held zero very well. Now that is only a .22 Mag but mounted on the slide it gets some pretty violent slamming in both directions. I think they hold up well because, being so light (less than 2 ounces) there is little inertia and they have only the one lens to keep anchored. Adding the Fastfire cut my group size in half or better, compared to the iron sights, even though the AMT came with very good irons.