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Dueling Rifle Rounds: It’s All About the Wound Channel

by Greg on May 25, 2010

The Times (the British one) has a story about the continuing debate over the 7.62mm round versus the 5.56mm as employed in the long range firefights in Afghanistan. The story asserts that the 5.56mm round used in the M4 rifle “lacks sufficient velocity and killing power in long-range firefights.” As Defense Tech readers know, we’ve covered this issue before.

As for the stopping power of the 5.56mm round, that very topic came up at a roundtable discussion I attended with the Army’s Program Executive Office Soldier last month at Aberdeen Test Center, Md. It led to an interesting discussion about wound dynamics, the “wound channel” and the “bleed out effect.”

Responding to claims that high-velocity 5.56mm rounds pass straight through the body without killing, Brig. Gen. Pete Fuller, the commander of PEO Soldier, said a new 5.56mm round that will be shipped to troops beginning in June, the M855A1 lead free slug, will get rid of what he called “yaw dependency.”

“The current M855 (5.56mm) ball round is yaw dependent. The closer you are to something you’re shooting at, the less yaw it has and it’s going to go right straight through,” said Fuller. Also, the M4 carbine has a 14 ½ inch barrel compared to the 20-inch barrel on the standard M16. “That shorter barrel cut out 5 ½ inches for that round to get to full muzzle velocity,” he said.

Col. Doug Tamilio, project manager for Soldier weapons with the PEO Soldier, discounted the reports of multiple 5.56mm rifle rounds penetrating straight through enemy bodies, “If you look at the bone mass of the human body, there is a lot of bone, if you hit a bone, [the bullet] is not going through the body, its putting an individual down.”

Knockdown is actually a misnomer, said Lt. Col. Christopher Lehner, program manager for individual Soldier weapons at PEO-Soldier. “You generally don’t knock anyone down, unless you have a very, very large round and you hit bone.” What typically brings down a human being when hit with a bullet is the “bleed-out effect”: massive blood loss that causes the body to shut down, the person staggers and then collapses.

When the 5.56mm high-velocity round enters the body it creates a “wound channel,” Tamilio said, “that wound channel as it expands and contracts it causes the bleed out effect.” A high-velocity 5.56mm round creates a sizable wound channel, he said, big enough to do the job.

More important than the size of the rifle round is the individual’s marksmanship, said Lehner. The critical area on the human body is only about six inches wide extending from the top of the head to the lower abdomen where vital internal organs and nerves are clustered. “You hit there, the guy’s going to bleed out a lot quicker.”

Lehner explained the importance of training like this: Take two soldiers. One of whom is fresh out of basic training and equipped with an M-4 rifle with all the high speed sites. The other is a special operations soldier carrying only a 9mm pistol. Who would you choose to go through the door first?

More often than not, “you’d have the special forces guy go through first, because he knows where to place that bullet very quickly and he’s shot thousand of rounds so he’s got that training and confidence to go in there with a weapon that some soldiers might think is only a paper weight.”

– Greg Grant

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