In order to participate in the GunBroker Member forums, you must be logged in with your GunBroker.com account. Click the sign-in button at the top right of the forums page to get connected.
Options
How well do you know your gun powder?
wallie
Member Posts: 12,171 ✭
Comments
doubt it in that caliber
First, it must be understood that recovering vertically fired bullets is difficult because wind causes them to drift from the expected vertical line. (This probably accounts for many of the myths.)
Hatcher's tests indicated that on the average, vertically fired rifle bullets reach about 9000 feet in altitude (slowed from their muzzle velocity by air drag and gravity to zero velocity), taking about 20 seconds to reach maximum height. Then, pulled by gravity, and slowed by air drag they take about 40 or so seconds to return. Bullets fired vertically come back base first. Why? Read on!
Hatcher describes one experiment with the 150gr M2 Ball bullet fired vertically. When it came back from vertical (round trip time was about 42.9 seconds) it left only a 1/16 inch dent in a soft pine board that it happened to hit. (Not exactly what it would do at 2700f/s, eh?) Based upon this and similar tests Hatcher concluded that the impact velocity was about 300 f/s, which from additional testing appears to be the terminal velocity (the maximum free fall velocity which is limited by air drag on the body in question) of that bullet falling from any height in the atmosphere. (If I remember correctly from my limited parachuting experience the terminal velocity of a falling person is somewhere around 130 mph or about 200 f/s.)
What does not substantially change, even at extreme range, is the rotational speed of the bullet that was imparted by the rifling (around 300k rpm) since the effect of air drag on the rotational velocity in negligible. Thus the gyroscopic action, once the projectile is stabilized, tends to keep the bullet oriented in the same direction, thus the base first (well ok, original position trailing end) return. It is interesting that this was not commonly known until just before WWII. The British had lots of dud antiaircraft rounds that all came back base down, or more correctly oriented to the same elevation as shot from the gun. BTW, this is what raises hob with traditional long range small arms ballistics. With lots of elevation on the bore (past 2,000+ or so yards) at the far end many bullet are actually falling sideways and all frontal air drag algorithms are out the window.
Interestingly, Hatcher describes an experiment that shows the gyroscopic stability at work. They loaded the 150gr M2 flat based bullet backwards and found that the round trip time was a bit shorter (about 30.4 seconds) due to the bullet being "streamlined (point down) on the return trip. The drag on the upward trip was not as greatly effected due to the high muzzle velocity. No estimated impact velocity was given but it probably would have been somewhat higher due to the lower air drag on the bullet since it was coming down point first.
The Haag article used a ballistics computation program to calculate vertically fired bullet performance and came up with results comparable with Hatcher's work. Using bullets ranging from the .22 rim fire to the 180gr .30 caliber spitzer in the .30-06 the time of flight (up & back) ranged from a low of 25 seconds for the .25ACP to a long of 77 seconds for the M193 ball. Maximum altitudes ranged from a low of 2288 feet for the .25ACP to a high of 10,103 feet for the 180gr .30-06. Terminal velocities ranged from 134 f/s for a tumbling .22 Short to a high of 323 f/s for the 180gr .30-06.
Haag calculated the performance of the .30cal 150gr M2 ball round fired by Hatcher as a maximum altitude of 9330 feet and a round trip time of 57 seconds which is, for all intents and purposes, the same as Hatcher's observations.
As a point of interest, a velocity of about between 180 and 360 f/s (?) is needed to penetrate skin. The wide range comes from the non-uniform strength of normal skin tissue. Projectile shape has no statistically significant effect on the penetration. However, one could still be seriously injured if struck by a falling bullet even if it doesn't break the skin.
Those interested in learning more about vertically fired bullets may want to obtain a copies of Hatcher's Notebook and the Haag article.