I highly recommend this - Leapers UTG Remington 870/1100 Picatinny Claw Mount

All I wanted was a scope mount I could attach to the frame of my new shotgun. The clip-on ones are usually a waste of money, and the high class ones require drilling and tapping the receiver.

This scope mount combines the best of both worlds. It is a close enough fit that I don't expect the sight to move. Then there are the mounting pins, replacements for the factory pins, that remove all doubt of the mount moving. Pushing the mount into place left me concerned because this thing goes on tight. However, having gotten it into place, it left no scratches.

Installation took me about ten minutes. When I do it on my next shotgun, it should take closer to two.