I agree with using Leupold. I have two 742's, (Rifle, and Carbine) both with Leupold bases, and rings. No shimming required. I also used in the past, on another 742 I have since sold, a Redfield J R base, with Redfield rings. This setup is almost identicle to the Leupold Standard base and rings. No shimming on this one either. These 742's all/were .30-06.