17 hm2
Just mount a scope on it, take it gopher hunting, and try to keep the stupid grin off your face.
After you use the 17HM2 for a while, you will become a fan of it. It is a very under rated cartridge. Everyone tends to compare it to the 17HMR, but that is like comparing the .22 Long Rifle to the .22 Magnum.
You should find that the 17HM2 is a very accurate calibre. It is a good 125 yard rifle on Gophers, and 150 yards is within it's capability. It is also effective on larger varmints, such as Coyotes and Raccoons with a proper hit on them. The cost of the ammo is about half of what the 17HMR will cost you. However, it takes a bit more effort to find ammo than the .17HMR, so buy a brick at a time. It is quieter than the HMR, and the bullets do not tend to ricochet like the .22 LR sometimes do. It is an ideal cartridge to use in more populated areas. I have also found that if you show it to landowners when asking for permission to hunt, I have a better chance to get on their land. People tend to think that the smaller bullet will be less dangerous, and if you explain the tendency to break up, and the safer shooting that can be done with it, they can see it your way. After all, what can happen with that itty wee bullet?
Here in Manitoba, .17HM2 ammo is about $6.90 a box, or about the same price as lower end Target ammo, but .17HMR is between $15 and $19 a box.
You got a good deal on the rifle.