.172 is 4.37mm. I started off years ago, using a .220 Swift, then switched to a .17Ackley Bee as I wanted to see every impact, then .17Remington which shot this gopher in the picture - 380yards IIRC, to my current .17Ackley Hornet and .17HMR.

We use the rimfire .17Hornady's to 200yards - head and chest shots - bipods off tables or our quads boxes, and the centrefore .17's from there on out. Most of our CF shooting now is under 400yards at the farms/ranches we shoot.

There are rimfire areas as well, where the Ruger 10/22's with custom barrels and 25 round mags come into the fray. A 7 day 'shoot' is usually good for 1,000 to 1,500 gophers each. It's a lot more laid back than shooting them in the prairies, where 500 shots a day are the norm & the Alberta and Sask. rats are smaller, too.