That's one of the downsides to that kind of mount.. My only suggestion is to hand fit, with a file, the mounting bar into your carry handle... some of the aftermarket ones don't allow it to seat into the carry handle groove for a solid fit and it will start to loosen after a few rounds..You can file it down carefully for a good fit..
The only one I ever used that fit well was the one than came with my 4x Colt scope with my SP-1 model Colt.. If the rifle had shot well with factory ammo, I would probably still own it..but that was 20 years ago and .223 quality factory ammo was kind of rare at that time..
