50 BMG case weight/damage from falling

[mokin]

Cool photos. Thank you, guys. Nobody has the math chops to try to tackle the question about the impact force of a .50 BMG case falling five miles? I'm still interested.

I think I formed this question after hearing some of the stories I heard from a guy I worked with whose father flew a P-47. I was thinking more about structures and livestock. From what has been posted so far, it sounds like my calculations are off some.

I had a Great Uncle who flew a P-38 in Europe. He was shot down in 1944 and spent the remainder of the war as a POW. I found the Missing Aircrew Report regarding him. I never heard him talk about it, but this roughly matches what my grandfather told me.





Because this may be drifting away from firearms, I do have a couple of family heirlooms from him. But I've posted those pics at least once here on some thread or another already.

 

[mokin]

Geez this got me wondering. How many rounds on average did a single heavy bomber use on a typical run over enemy territory? I would think US ones would be more with daylight raids vs the Brits at night.

Depending on the station, they carried between 400 and 500 rounds.

In the Mojave desert you can still find .50 BMG cases with 43,44, and 4 headstamps.

If you find two cases close, you draw a line between the two, then go down the line the same distance as the distance between the first two cases and find another, and another, ect.

If you look close you can also find link on the line.

If you really look hard, especially in sand dunes you also find projectiles.

I think they used the dunes (Stovepipe, Panamint, Saline, Ibex, Eureka.....) to see how the guns were regulated, the whole area was closed for training during WW2.

I've seen this at Fort Carson and Kaho'o'lawe as well. The links are easy to find on hardpan.

"There's plenty down in the low desert also, between Niland CA and the AZ border."

One of my favorite finds out in the desert was a .50 BMG projectile coming out of the sand 15 yards away from a large atlatl point also coming out of the sand.

I can just see a future archeologist.... Ummm, no wonder they lost!

Having been in the impact areas as part of EOD and as an archaeologist, i have seen this. It is rare to find a point, but there is plenty of evidence in the form of chipped stone and hearths.

 

[lysanderxiii]

Well. I know you don't want to be anywhere under a helo at any altitude when a minigun is going off- those 7.62 casing are HOT and there's a lot pouring out. Also, I came across the 30mm casings that drop from the A10's when they do a gun run, but those runs were always done across the front of our positions at the enemy at low altitude, plus they explode on impact- need a standoff from that just so you don't get hit by secondary projectiles from all the explosions- wouldn't want to get hit by the brass either though- they come on low but they are moving fast.

The GAU-8 gun system in the A-10 is what is referred to as a double-ended feed system, that means the empties are returned to the back of the feed drum. Nothing is dumped over-board.



The only 30mm cannon I know of that dumps empties over-board is the AH-64 Apache

 

[.308 Norma]

Just for fun, I did some math and came to the conclusion that an 850 grain piece of brass would reach a terminal velocity of 133 ft/s and impact with 33 ft/lbs of force.

Nobody has the math chops to try to tackle the question about the impact force of a .50 BMG case falling five miles?

A "terminal velocity" of 133 ft/s is a little over 90 mph. I still say an 850 grain piece of brass falling at that speed would have less "impact" than it would have if a B-17 ran into it at a B-17's normal cruising speed (I googled it) of 170 mph.

 

[lysanderxiii]

************

 

[lightman]

Amazing, a lot of these service guys were 18-19-20-21 years old, just a different breed of people then. great photos!

They truly are the greatest generation!

 

[lightman]

I'm going to need a citation for that second picture please. That is quite something.

I usually put a "like" on photos but I just can't bring myself to do so on those damaged planes!

 

[mokin]

A "terminal velocity" of 133 ft/s is a little over 90 mph. I still say an 850 grain piece of brass falling at that speed would have less "impact" than it would have if a B-17 ran into it at a B-17's normal cruising speed (I googled it) of 170 mph.

No doubt you are correct. Especially when things get cattywhampus as shown in some of the pics posted earlier.

 

[lysanderxiii]

Nobody has the math chops to try to tackle the question about the impact force of a .50 BMG case falling five miles? I'm still interested.

The terminal velocity will decrease as the object falls due to the air becoming more dense. Assuming your weight is close, the velocity profile will be something along the lines of:

20,000 ft - 17.5 mph
15,000 ft - 16.0 mph
10,000 ft - 14.8 mph
5,000 ft - 13.7 mph
2,000 ft - 13.1 mph
1,000 ft - 12.9 mph

Now, it will take some time for the case to slow down as it passes through the denser air, so it might hit the ground at 10 to 12 mph.

(Estimated using the drag coefficient of a cylinder falling base (heavy end) down with a length-to-diameter ratio of greater than 2, which is around 0.8)

 

[HPJeep]

I found a 50 BMG that failed to fire that fell out of a plane near Rawlins Wyoming back around 1982. Been out in that high desert for some 40 years before I found it while looking for arrowheads.

 

[FL-NC]

The GAU-8 gun system in the A-10 is what is referred to as a double-ended feed system, that means the empties are returned to the back of the feed drum. Nothing is dumped over-board.



The only 30mm cannon I know of that dumps empties over-board is the AH-64 Apache

Then they must have came out of the apaches- remember that we were a safe(ish) distance from whatever was getting dropped- and some of our TIC's looked like a live fire airshow, depending on what was sent. So yes, there were occasions where apaches and A10's were on station, obviously not slinging ordnance at the same time. Driving out after, I just assumed they were from the A10's.

 

[mokin]

The terminal velocity will decrease as the object falls due to the air becoming more dense. Assuming your weight is close, the velocity profile will be something along the lines of:

20,000 ft - 17.5 mph
15,000 ft - 16.0 mph
10,000 ft - 14.8 mph
5,000 ft - 13.7 mph
2,000 ft - 13.1 mph
1,000 ft - 12.9 mph

Now, it will take some time for the case to slow down as it passes through the denser air, so it might hit the ground at 10 to 12 mph.

(Estimated using the drag coefficient of a cylinder falling base (heavy end) down with a length-to-diameter ratio of greater than 2, which is around 0.8)

Cool. Your table demonstrates an almost 30% decrease in velocity due to air drag. I used a constant drag coefficient of 2.8125 in my calculations. I figured air density would slow the fall but didn't include it in my final calculation of 33 lbs.

Having climbed 14,000 ft mountains I can attest to the "sparsity" of air at that altitude. I read that the changing density of air was a major concern when taking shots with the Paris Gun in WWI (but I digress)....

 

[Mark_Mark]

Then they must have came out of the apaches- remember that we were a safe(ish) distance from whatever was getting dropped- and some of our TIC's looked like a live fire airshow, depending on what was sent. So yes, there were occasions where apaches and A10's were on station, obviously not slinging ordnance at the same time. Driving out after, I just assumed they were from the A10's.

Always wanted to know… does the A10 dump there 40mm brass or collect it in the fuselage?

 

[Mk-211]

The 30mm gun on the A-10 holds the spent cartridges.