Can someone tell me how much damage can the M1 Garand do when it hits a body and how?

Well, that depends on a number of factors. But, in a very general description the following is realtively accurate:

A 180 grain .3006 copper jacketed lead round travelling at sonic speeds will upon striking a person in say the chest, leave an entry wound slightly larger than the bullet itself. The wound channel through the body will be relatively linear even if hard bone is struck. Unlike the lighter .223 round in a M16 the .3006 round has sufficent mass and velocity to remain fairly linear in its travel. That wound channel, so long as the bullet remains sonic, will be about 3 to 4 times the bullet diameter disrupting all soft tissue along the track of the bullet. At sub sonic speeds the wound channel will reduce to slightly larger than the round itself.
If on entry or in travelling through the body the jacket seperates from the bullet (a frequent occurance) the jacket typically flower back and may fragment causing a primary wound channel for several inches 3 to 4 times the bullet diameter and any fragments may travel anywhere up to a foot or more from the original track causing an additional wound channel. In these cases the lead portion of the bullet may mushroom increasing the diameter of the wound channel as well.
The exit wound will be about twice to three times the bullet diameter with significant disruption of the skin in the area of exit. In most cases bleeding is limited to internal areas primarily so there is not alot of blood to see on the individual.

ah, those are nasty bullets, i got a .357 magnum with the hollow bore bullets, and that thing will do some damage even for a pistol

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