These have gotten bad reviews because these current mounts 459 tend to wiggle when on the gun. I was told that the older discontinued 457 mounts didn't do that. These are a cheap way to mount optics on your Crosman multi pump 1377 ect and CO2 (2240) ect with out buying and installing a steel breech. You have to shim the bottoms of the mounts. Do this and they are rock solid. First thing you do is take out the cheap Chinese screws that can strip in the head and replace with American made screws. The size is 3mm x 16mm. Then buy a roll of magnetic tape with adhesive on one side. Cut off a piece about 1/8th wide and trim one end to fit the bottom of the mount. Put tape on each side of the tube below the barrel where the mounts will go. Set mounts in place and tighten down. With the tape shims the mounts are rock solid and you should be able to mount any optic to them.