 The lightweight bullet of 1.58 grams / 24.4 grains reportedly achieved a muzzle velocity of about 1,000 m/sec / 3,270 ft/sec and a muzzle energy of 790 Joules / 583 ft lbs.This claim contrasts sharply with the comparable, more modern .17 HMR which has a muzzle energy of 340 Joule / 250 ft. lbs.Due to the combination of a thin-walled rimfire case with a high-pressure powder charge, the cartridge needed good external support so the MKR rifle was designed to use locked breech, gas-operated action with a vertically tilting bolt rather than straight blow back operation.