[E.J.W.]

Thanks for the replies. I will go with the 40mm. I already have a base and rings that fit this rifle. I don't think the rings are tall enough for the 50mm anyway.
Peetsakiller, why a 243 you ask....
I was given the rifle a few years back. I have not done anything with it except keep it clean and oiled. I do shoot woodchucks off my deck in the backyard with my ruger 10/22 all summer long. Most are under 100 yrds.
With this 243 I plan shooting some woodchucks and maybe a coyote or two at 150 acres of farmland I recently gained permission to hunt on. I may have spoke a bit short in my opening post regarding the yardage. Range is likely to be a bit farther at the farmland now that think about it. More along the lines of 150 yards or so. I want to start out by taking the farthest shots offered just because this caliber is capable of it.
Thanks for the interest.
E.