Embed it self grenades don't explode on impact

a 40 mm grenade has to spin a number of revolutions to arm. I have actually seen this very thing happen. They guy took a hit in the thigh. It broke the skin, but didn't become embedded. His femur was fractured (not completely broken in two, just cracked) and the skin split about 4 inches and bled. EOD got rid of the unexploded grenade.

the 40mm grenade doesn't arm until after 5 meters of flight. if it hits a target closer than that it will not explode. I don't think it has enough energy and velocity to penetrate the body. After 5 meters it would explode on what ever target it hits.

kuyakev, Darn good question. The various 40mm grenade rounds (HE etc.) fuses arm only AFTER 14 to 28 meters from the muzzle, (This does not apply to Less-Than-Lethal projectiles.) and thus would NOT explode on impact until beyond these distances. M406 40 mm HE (high explosive) grenades fired from the M79 travels at a muzzle velocity of 75 to 78 meters per second (About 260 fps.) As a comparison, a 1920 U.S. Army Ordinance study results concluded that a .30 cal. 150 gr. bullet at the velocity of about 420 fps would yield the 60 foot pounds of energy to produce a disabling wound. That same bullet traveling at 300 fps = an energy of only 30 foot-pounds. HOWEVER the 40mm round is MUCH heavier (has more mass) than the .30 cal. bullet and is at nearly equal velocity. It thus would strike with much more force. Even considering it's substantially larger frontal area it would be at least disabling if not lethal. Of course, LETHAL 40mm rounds were developed. For close range fighting two styles of M79 rounds were developed. The first was a flechette or Bee Hive round which fired 45 10-grain steel flechettes. (Flechettes proved to be ineffective because they would often not hit point-first and penetrate. Instead they would hit sideways and bounce off.) About 1966, this was replaced by the M576 buckshot round. Containing twenty pellets of #4 buckshot (M576E1) or twenty-seven pellets of #4 buckshot (M576E2), this round could be devastating at close ranges. See:FM 23-31 Hope this helps.

It depends on the distance. I assume you meant a fused, explosive round. Within 5 meters it will disarm if it strikes anything, a safety mechanism. The round is too slow and large to penetrate the body. It could break some bones, maybe shatter the skull at close range, but will not explode within 5m of the muzzle. Greater than 5m there are some rounds that are impact-fused and those would explode if hitting a person, or any object. +5