I've got a Gamo 220 that shoots 1000fps

I have killed countless squirrels with it and also two raccoons. Don't have to be real close to get the job done with this gun, but with its wierd recoil I can't get a scope to stay on it. The scope mounts slowly slide in the dovetai until they finally slide out the back which screws them up. Ive tried steel and aluminum with no luck.
By the way; its .177 caliber and what makes it really nice is it is break over, which means you break the barrel down, insurt the pellet, break it back and its ready to go(no pumping)