Gene is right. If you want a good scope mount for a 870 or 1100, buy a barrel such as a Hastings with the Cantilever mount. That puts the scope where it should be instead of hanging on the receiver pins. Just my opinion anyway and yes i have used the saddle type. The saddle mount i had on an 870 Wingmaster never seemed tight.
My honest suggestion would be to go by you an H&R Ultra Slug Hunter in either 12ga or 20ga. I have the 12ga and its basically a 10ga barrel blank drilled for 12ga which makes it sort of a Bull Barrel slug gun. About the most accurate slug gun with Sabot slugs money can buy. I paid around $285 5 or 6 years ago. For the price it can't be beat. I use the 300gr Hornady SST slugs.--Matt