Introduced a couple of years after the .17 Hornady Magnum Rimfire (HMR), the .17 Mach 2 may be the most underrated small-game load going. From a rifle, the HMR is simply too destructive for squirrel hunting. But the Mach 2—based on the .22 Long Rifle case with a 17-grain bullet—tends to punch a tiny entry hole, cause massive internal damage, and never exit. It's flat shooting beyond 100 yards, too. The ammo is difficult to find and expensive, but in this day and age of obscene .22 LR prices, it's nothing a serious squirrel sniper can't accept. —W.B.