The .17 HM2 is based on the .22 Long Rifle "Stinger" case, necked down to .17 caliber (4.5 mm) and using a bullet weighing less than half the weight of a typical .22 Long Rifle bullet.

The weight of the bullet is a key part of achieving a very high velocity for a rimfire round.

[2] The .17 HM2 may or may not live up to its "Mach 2" name, depending on geographic location and conditions, with velocities out of a rifle of 2,100 ft/s (640 m/s).

[3] The velocity is nearly double that of a standard .22 LR, which results in a much flatter trajectory out to its 175-yard (160 m) effective range.

The higher pressure makes conversion of semi-automatic firearms more difficult, as virtually all are blowback designs that are sensitive to pressure changes.