Well since it is now .22 lr only, that's what to use.
For those of you recommending the .17 HMR, what's the largest beaver you have ever seen? I am wondering if maybe you think that they are all in the 10 lb. range or so. Biggest one I have seen in Nebraska was 53 pounds. I have seen pictures of beaver in the Upper Peninsula of Michigan that the trapper said went just shy of 70 pounds.