I have a Walmart Mark II-F that has standard 3/8" scope grooves, but is NOT drilled for other bases. I tried a set of 2 pc rings (Weaver Brand) for 3/8" grooves and 1" scope tubes, but it walked completely out of the grooves within 10 shots -- apparently they are NOT made for heavy 4x16x40mm AO scope I mounted.

As an alternative to having the rifle drilled for bases I've ordered a set of 2 pc clamp on Weaver adapters (see URL below).

http://www.straightshooters.com/bsqu...averbases.html

It looks like they will fit the Mark II well and give me full grip on the existing groove length while providing a standard Weaver style scope base. Has anyone tried these?