I'm partial to the .17 HMR because I recently bought one and I love it. Very accurate, and smokin' hot muzzle velocity. That being said, I read some comparisons online between the .17 HMR and the .22 mag. They're comparable, although each has it's advantages over has advantages over the other. It kinda depends on what your looking for. The .22 mag apparently hits somewhat harder out to 100 yards. Some say it does more damage. The .17 HMR has more range and accuracy, probably the best you can get from a rimfire in my non-expert opinion. It's probably a bit more wind-sensitive than the .22 mag because it's a very small bullet (only 17 grains). However, that little bullet shatters on impact, causing alot of damage. I would imagine this would cut down on ricochets too, at least off hard surfaces. My .22 LR is famous for that. You hear "pings and buzzes" pretty often. Anyway, go to this link, www.shootingsquirrels.com/17hmr
, and check out the videos. Make sure you screen them first or turn down the sound if you have kids around because some of them have songs with obscene language. Looks like it must have been some little immature knotheads that put the videos together, with garbage like that, but the videos themselves are pretty cool. The one with the ground squirrels is ok. Anyway, I hope this helps you out. Good luck nailing those nutrias! I understand you have to have a trapping license, but you can get paid somewhere around $6.00 - $8.00 apiece, last I heard, for each nutria you kill. Probably pay for your license in no time.