The .17 HM2 operates at relatively low velocities, and for this reason, its bullets leave very little copper jacket fouling in a barrel with a smoothly finished bore. However, it will build up rather quickly in a rough bore.

I have yet to use a copper solvent in my match-grade barrels, but fouling of another kind will need to be kept under control regardless of the condition of the bore. Due to the relatively slow burn rate of powders loaded in the .17 HM2, propellant fouling seems to build up faster than with .22 LR loads. I do not find the buildup from a couple hundred rounds to have a detrimental effect on accuracy, but it tends to accumulate rather quickly in the chamber. So to assure reliable functioning of an autoloader, it will need to be cleaned more often than a bolt-action rifle. The best bet is to clean with a good powder solvent every 250 to 300 rounds, and since a slight amount of wear or damage to the rifling at the muzzle can harm accuracy rather seriously, a pull-through cleaner is the way to go. The bores of other types of rifles are best cleaned from the chamber end, and a cleaning-rod guide should be used to protect the rifling at the throat from wear.

Ballistic coefficients for the 17-grain bullet of the .17 HM2 and the 40-grain bullet of the .22 LR are close to the same, but the .17-caliber bullet shoots flatter because it starts out considerably faster. Its high velocity also enables the .17-caliber bullet to deliver the same energy levels downrange, even though it is 35 percent lighter.

The .17 HM2 strikes a 100-yard target with around 90 foot-pounds of punch, which is about the same as for both high-velocity and hypervelocity loadings of the .22 LR. However, it does fall short of the 110 ft-lbs delivered at that distance by the CCI Velocitor and its 40-grain bullet at 1435 fps. Also, I have found the .17 HM2 to be less sensitive to wind than the .22 LR Stinger.

Within its effective range, the .17 HM2 offers plenty of punch for hunting small game. Fox squirrels are tough critters, but the first two I toppled from the limbs of the same tree appeared stone dead before they reached the ground. Both took a 17-grain bullet through the lungs at exactly 61 yards, and damage to the eating part was no worse than with .22 LR hollowpoint ammo.

Over the next few days, I made body shots on quite a few more of those big, fat critters, with some shots as far away as 125 to 130 yards. While I did not lose a single one, I could tell I was beginning to push my luck at those distances. Based on my experience, I'd say the little cartridge begins to run short on steam at about 100 yards for body shots on game the size of a fox squirrel.