Suggestions for good scope rings

[7man]

Went to rifle range, shot some steel at 500, and was very dissapointed with my loads. I could'nt hit for nothing. I thought I needed to work up some new loads or something. Then, when I was cleaning my 7 RUM the next day I noticed my scope had slid as far forward as it could possibly go through the rings. The rifle took a good pounding in the lead sled I guess.

What I have for a setup is a Nikon Buckmasters 3-9 to match a Savage 110 with a EGW Picatinny rail. I would love to know what I should get for picatinny rings and the proper way to install these.

Any input would be great. I'm new to shooting magnum loads let alone an overbore one.