Re: ruger 1000yd. rings
Burris rings with the offset inserts. You can get up to 40 MOA worth of inserts for them, that's what I have on my Ruger 416.
Using the inserts, you can get anywhere from 5-40 MOA of slope out of them, the inserts are in 5 MOA increments basically. The 20 MOA inserts are sold seperately, although they come with the 5's and 10's, so you can get 15 MOA total with that out of the box combo. I'd buy two sets of 20 MOA inserts along with them so you're sure to have what you need, just install those two sets for 40 MOA total just to be safe. You may only need 30, or even 20 is all, but you'll have them if you need them.