Does not hold zero on 10mm glock g20/g40 - Crimson Trace CMR-203 Rail Master Green Laser Sight - Universal

From a rest this took far too many shots to sight in at 50 feet which is where it is supposedly zeroed from the factory. Then after 6-7 shots it would lose it's zero. I had several other shooters try it one was a champion bulls eye shooter on the club pistol team and if a competition bulls eye shooter has problems then I know it's the laser. The iron sights are dead on and the guy made a ragged hole with the iron sights and yet with the laser the shots were all over the place, same box of ammo. Maybe mine is defective, but I have lost all confidence in using a laser considering I can shoot small 2" groups at 50 feet without even trying with my red dot.