[Bilge_Rat]

I was not talking about all rounds, I was talking about military 7.62mm/5.56 mm.

a straight through shot will enter and leave the body leaving just a small hole, obviously if it hits a bone or major organ or shatters, that is a different story.

It is more of an issue with a new type of 5.56 mm ammo. There has been criticism that it is not as effective as the older round.

Combat operations the past few months have again highlighted terminal performance deficiencies with 5.56×45mm 62 gr. M855 FMJ. These problems have primarily been manifested as inadequate incapacitation of enemy forces despite them being hit multiple times by M855 bullets. These failures appear to be associated with the bullets exiting the body of the enemy soldier without yawing or fragmenting.

http://en.wikipedia.org/wiki/5.56%C3%9745mm_NATO

some have theorized that this is caused by the fact that Taliban fighters are malnourished and very thin, so the 5.56 mm ammo tends to go through as a clean through and through.

most of the damage caused by 5.56 ammo comes from tumbling and/or shattering inside the body.

There has been much criticism of the allegedly poor performance of the bullet on target, especially the first-shot kill rate when the muzzle velocity of the firearms used and the downrange bullet deceleration do not achieve the minimally required terminal velocity at the target to cause fragmentation.[23] This wounding problem has been cited in incidents beginning in the Vietnam War, first Gulf War, Somalia, and in the current conflicts in Iraq and Afghanistan. The change of the original 1 in 14 inch barrel twist rate of the AR15 to the 1 in 12 inch barrel twist rate in the M16 and XM16E1, resulted in greater long range accuracy and better bullet stability. However, it also resulted in making the bullet less likely to tumble on impact with soft tissue. Much of the spectacular wounding ability of the original AR15 in the Vietnam War was on account of the 1 in 14 twist and the bullets tendency to tumble and possibly also fragment after impact. In recent lab testing of M855, it has been shown that the bullets do not fragment reliably or consistently from round-to-round, displaying widely variable performance. In several cases, yawing did not begin until 7–10 in of penetration. This was with all rounds coming from the same manufacturer.[23] This lack of wounding capacity typically becomes an increasingly significant issue as range increases (e.g., ranges over 50 m when using an M4 or 200 m when using an M16) or when penetrating heavy clothing, but this problem is compounded in shorter-barreled weapons. The 14.5 inches (37 cm) barrel of the U.S. military's M4 carbine generates considerably less initial velocity than the longer 20" barrel found on the M16, and terminal performance can be a particular problem with the M4.

The original russian made 7.62x39mm rounds used in Vietnam in AK-47s were too stable, they tended to go straight through and through and cause only a small wound:

Although the new cartridge represented a great leap forward from previous designs, the initial bullet design was flawed. The complete solidity of the M43 projectile causes its only drawback—it is very stable, even while traversing tissue. It begins to yaw only after traversing nearly 26 cm (10 in) of tissue.[4] This greatly reduces the wounding effectiveness of the projectile against humans. These wounds were comparable to that of a small handgun round using non-expanding bullets. Unless the round struck something vital, the wound was usually non-fatal, small and quick to heal.

http://en.wikipedia.org/wiki/7.62%C3...ese_steel_core