Falling Bullets

We have a story here in Atlanta:

Marquel was seated next to his mother, Nathalee, while those in the church waited for a 12:30 a.m. concert to begin. Then, those in the sanctuary heard a loud pop. It was almost like the sound of a balloon.

Instantly, Marquel was on the floor, and he was bleeding.

An X-ray at the hospital confirmed that it was a bullet that struck Marquel, his uncle said. Doctors at the hospital had hoped to do surgery on the child, but it was too late.

Investigators returned to the church later Friday, where they discovered the point of entry for the bullet: in the roof of the church. Phipps said police believe someone fired a celebratory shot into the air, and it went through the roof on its way down.

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Ok, there's something that doesn't add up for me. I understand that a falling bullet could hurt you, even maybe kill you. I don't see how a free-falling bullet could penetrate a roof (shingles+plywood+insulation+drywall) and then have enough energy left to penetrate a skull, even a 4-year old's skull.

My suspicion is supported by a study done during WW2:

1. Hatcher's Notebook on Falling Bullets
typed by Norm Johnson (njohnson@nosc.mil)

From Hatcher's Notebook:

"Among the many experiments carried out at Miami and Daytona, was this same one of vertical firing. It was desired to find out how fast a bullet returned to earth and how dangerous such a bullet would be if it struck a soldier after dropping from a great height. Many interesting things were learned from this test, and they are given in detail in the "Official Report of Vertical Time Flight for Small Arms Ammunition," in the files of the Ordnance Department. Much of the information given below is from that source.

"At Miami the firing was done from a platform built in the shallow water of a protected inlet, where water was often calm. A frame was built to hold a machine gun tripod so that the barrel pointed vertically. Instruments were provided to check the angle of the barrel, and the tripod controls permitted any necessary changes in the barrel inclination to be made with ease and precision.

"Out of more than 500 shots fired after adjusting the gun--only four shots hit the platform. One of the shots was a service 30.06, 150 grain flat based bullet, which came down base first...it left a mark about 1/16 inch deep in the soft pine board.

"Two more bullets struck in a pail of water and left only a perceptible dent in the bottom of the pail. One struck the edge of the thwart (seat across a boat, used by an oarsman) in the boat, and left a shallow indent...The last two bullets were 175 grain boat-tailed.

"It was concluded from these tests that the return velocity was about 300 feet per second. With the 150 grain bullet, this corresponds to an energy of 30 foot pounds. Previously, the army had decided that on the average, an energy of 60 foot pounds is required to produce a disabling wound. Thus, service bullets returning from extreme heights cannot be considered lethal by this standard.

"Most .30 caliber bullets seem to attain this final velocity, and it doesn't make any difference how far they fall. Even if a bullet was fired downward from a very high plane, it would still reach the ground at the same velocity. That is because the resistance increases very rapidly with increases in air speed. If the air resists the motion of the bullet a certain amount at 300 feet per second, it will resist three times as much at 600 feet per second and nearly nine times as much at 1000 feet per second.

"A 150 grain bullet weights .021 pounds, and when, in falling, it reaches a velocity where the air resistance balances the weight, the velocity of the fall will no longer increase.

"For a .30 caliber bullet of standard experimental shape, having a pointed nose of two caliber radius, the air resistance on the nose at 2700 fps. would be about 2.3 pounds; at 2000 fps. 1.5 pounds; at 1500 fps. .89 pounds; at 1000 fps. .17 pounds; at 500 fps. .04 pounds; at 350 fps. .025 pounds; at 320 fps. .021 pounds, balancing the weight of the bullet and stopping any further increase in velocity in the case of a falling bullet."

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Something about the local story just doesn't add up. Could it be that the shot was fired from a height (such as a tall building) down into the church?

For that matter, those in the sanctuary reported hearing a loud pop. This was not a bullet that was fired up in the air and free-fell into the church. Somebody inside that church fired that gun, or somebody on the roof.

UPDATE:
Ballistics came back:
“I would suspect this was a rifle. An AK-47. That’s the most prolific [weapon found] downtown,” said Kelly Fite, who was the top ballistics expert with the Georgia Bureau of Investigation’s state Crime Lab for almost four decades.
...But most likely, the shooter was about a half mile away and the gun was tilted at about 30 or 40 degrees, not straight up, he said.