the difference between a 17 and a 17 mach 2 is a 17 is a necked down 22 mag case and a 17 mach 2 is a necked down version of the 22lr. i have a 17 but it is expensive to shoot when a box of 50 costs $11. I would go with a 17 mach 2 if you are going for small game within 100 yards but DONT try to shoot a coyote with a mach 2. i have shot foxes with my 17 that have run for 100 yards when hit behind the shoulder. as a plus the 17 mach 2 shells are only $5-6 bucks a box of 50.