.50 Conundrum

[VaultBuster]

I've been perusing around a comment section and saw two people got into a debate. One was in defense of .50s and the other was someone who stated that American .50's were essentially trash rounds. He said, among a list of things, the incendiary charge in the bullets such as API actually were there just to make a flash, constantly compared .50 to 37mm high explosive muntions, and that the idea of burst mass didn't matter and was just a fallacy. He used the analogy, and I quote, "I can throw two tons of feathers at 1800 m/s at a tank and it wouldn't do much."

He also stated that .50's couldn't shear a wing off a fighter like the Bf-109 or Fw-190. Might I ask, is this all true? Was American .50's that terrible? I've tried to find gun cam footage and had trouble finding a good repository of where I can find footage that was correctly assigned, such as a kill assigned by a P-47 or P-51 without going through Youtube and making a blind leap.
I trekked through and could only find a manual about the .50 but everything else seems lost on my part.

I'm sorry if I posted this in the wrong section

 

[swampyankee]

Most of the people who post here are sensible, so their comments about the US 0.5 in will be more nuanced. The gun was certainly adequate, but not the best aircraft gun. Tony Williams, author of Rapid Fire, has some articles comparing aircraft guns on his website, BOOKS BY ANTHONY G WILLIAMS

 

[Shortround6]

I've been perusing around a comment section and saw two people got into a debate. One was in defense of .50s and the other was someone who stated that American .50's were essentially trash rounds. He said, among a list of things, the incendiary charge in the bullets such as API actually were there just to make a flash, constantly compared .50 to 37mm high explosive muntions, and that the idea of burst mass didn't matter and was just a fallacy. He used the analogy, and I quote, "I can throw two tons of feathers at 1800 m/s at a tank and it wouldn't do much."

He also stated that .50's couldn't shear a wing off a fighter like the Bf-109 or Fw-190. Might I ask, is this all true? Was American .50's that terrible? I've tried to find gun cam footage and had trouble finding a good repository of where I can find footage that was correctly assigned, such as a kill assigned by a P-47 or P-51 without going through Youtube and making a blind leap.
I trekked through and could only find a manual about the .50 but everything else seems lost on my part.

I'm sorry if I posted this in the wrong section

Well, a tank isn't quite the same thing
Very few aircraft carried even 1/2in armor (12-13mm) and even they did it didn't cover much area. There was an awful lot of area that had no armor at all.
.50 cal/12.7mm ammo would defeat most self-sealing fuel tanks. making a .50 cal hole vs a .30-.32 cal hole means the sealant has to move that much further to meet in the middle and seal the hole.

The .50 might not be able to blow a wing (or sizable piece ) off an airplane with one hit but it didn't have to. Think about what would happen if you took an electric drill to a wing spar and drilled several 1/2 in holes in places they weren't supposed to be and then tried to fly the plane at 300 mph and pull a several G turn.

Few .50s were operating on their own (defensive bomber guns aside) and multiple hits in a few 1/10s of a second can do a lot of structural damage. You didn't "drill" the hole, you "punched" it with varying degrees of tearing or stretching at the edges. Not to mention the effect of the impact on attachment points (like bolts through flanges).

Most US fighters (P-47 aside) carried 4 or 6 .50s, very few fighters of other countries carried more than two 20mm cannon and only a very few carried multiple cannon of larger caliber.

The .50 did have one of the highest velocities and had a very streamline bullet which meant it had one of the shortest times of flight to a given distance which made it easier to hit with, especially in defection shooting.


Like most things the truth is somewhere in the middle. The .50 was not nearly as good as some people claim but not nearly as bad as some of it's detractors claim.

The main problem with the .50 as an aircraft weapon was mainly it's weight and the weight of the ammo. By the time you got 4/6 guns with around 300 rpg you were carrying a lot of weight. The .50 was not particularly weight efficient but a battery of 4-6 guns was usually target effective on the targets it faced (very few 4 engine bombers)

There are a lot of old threads on this site that eventually get to basics of this question.

 

[swampyankee]

The USN, from what I have read, considered the 20mm to be three times as effective as the 0.5 in. Post-war, the Navy replaced the 0.5 in pretty quickly.

 

[mikewint]

Kind of a Lynx - Bengal Tiger comparison

 

[Greg Boeser]

One thing that is rarely mentioned is that .50 cal bullets do more than poke a hole through the skin of an airplane. They tumble. So the round might make a hole the diameter of my pinky going through the skin, but then it starts to turn over and rips through stuff on its way through. The bullet length is over 2" so that means a pretty big hole when it is parallel to the path of flight.

 

[Paul E.]

One thing that is rarely mentioned is that .50 cal bullets do more than poke a hole through the skin of an airplane. They tumble. So the round might make a hole the diameter of my pinky going through the skin, but then it starts to turn over and rips through stuff on its way through. The bullet length is over 2" so that means a pretty big hole when it is parallel to the path of flight.

One thing that is rarely mentioned is that .50 cal bullets do more than poke a hole through the skin of an airplane. They tumble. So the round might make a hole the diameter of my pinky going through the skin, but then it starts to turn over and rips through stuff on its way through. The bullet length is over 2" so that means a pretty big hole when it is parallel to the path of flight.

One thing that is rarely mentioned is that .50 cal bullets do more than poke a hole through the skin of an airplane. They tumble. So the round might make a hole the diameter of my pinky going through the skin, but then it starts to turn over and rips through stuff on its way through. The bullet length is over 2" so that means a pretty big hole when it is parallel to the path of flight.

One thing that is rarely mentioned is that .50 cal bullets do more than poke a hole through the skin of an airplane. They tumble. So the round might make a hole the diameter of my pinky going through the skin, but then it starts to turn over and rips through stuff on its way through. The bullet length is over 2" so that means a pretty big hole when it is parallel to the path of flight.

Important news! All spin stabilized projectiles tumble in the target! The reason is that for accuracy, the spin imparted by the rifling is chosen by & large by the desire to hit the target. So to hit a target at 1000 meters the spin rate is chosen based on stability of the projectile in air. As soon as the projectile passes from air into the different density of water, flesh, aluminum etc, the projectile becomes unstabile. It's just a physical fact. It's not a choice made maliciously, it's a beneficial result of the over whelming need to hit the target. A rather blunt .45 caliber pistol round tumbles at 900 fps by the same physics, just as does a streamlined .50 caliber at almost 3,000 fps.

If possible the spin rate is selected by accuracy requirements plus the desire for the tumbling to happen within the general thickness of a human body.

Paul

 

[Greg Boeser]

Does this count as being quoted 4 times?
The point I was making is that a bullet doesn't just make a neat round hole.
It might going in, but once it starts tumbling it will tear through everything in its path until it exits the structure, or all its energy is dissipated.
Now a .50 caliber bullet has a lot more energy than a .30 caliber bullet, about 5 times, so the amount of potential damage is significant, especially if it hits something solid, like a spar or engine block.

 

[CANRAY]

I've been perusing around a comment section and saw two people got into a debate. One was in defense of .50s and the other was someone who stated that American .50's were essentially trash rounds. He said, among a list of things, the incendiary charge in the bullets such as API actually were there just to make a flash, constantly compared .50 to 37mm high explosive muntions, and that the idea of burst mass didn't matter and was just a fallacy. He used the analogy, and I quote, "I can throw two tons of feathers at 1800 m/s at a tank and it wouldn't do much."

He also stated that .50's couldn't shear a wing off a fighter like the Bf-109 or Fw-190. Might I ask, is this all true? Was American .50's that terrible? I've tried to find gun cam footage and had trouble finding a good repository of where I can find footage that was correctly assigned, such as a kill assigned by a P-47 or P-51 without going through Youtube and making a blind leap.
I trekked through and could only find a manual about the .50 but everything else seems lost on my part.

I'm sorry if I posted this in the wrong section

Not to be a stick in the mud, but your friend and his feathers might want to study their physics some more. The idea of a ton of feathers must mean the mass and volume are contained. Then you're driving the contained mass at a tank at 1800 mps, or 5905.5 fps. Without question, the tank may still resemble itself but the crew inside would be nothing more than a sticky paste inside their demolished vehicle.
Perhaps your quoted friend meant to throw the feathers one at a time; but I've never seen a feather that weighed 2000 pounds.

 

[mikewint]

All spin stabilized projectiles tumble in the target! The reason is that for accuracy, the spin imparted by the rifling is chosen by & large by the desire to hit the target.

We need to straighten out some vocabulary:
1. SPIN STABILIZED - Modern bullets, conical shaped, are indeed given a spin along their longitudinal axis. This spin does indeed "stabilize" the bullet which means that tumbling is prevented. A tumbling object is rotating "end over end" creating tremendous drag and very little control over flight path, the smooth-bore musket for example.

2. SPINNING BULLET - a spinning bullet can be compared to a spinning top. If a top is made with some precision it will spin in a perfectly upright position, but, as the RPM slows it will begin to "wobble"; i.e. the end points begin to describe a circle around the center of mass. The correct term here is PRECESSION. The amount of precession for a bullet is dependent upon its uniformity and its rate of spin. Thus the center of mass of a spinning bullet keeps going along the path on which it was shot, while the tip is describing a small circle. This is less than ideal. An ideal bullet would be perfectly aligned with its course. Additionally as the bullet precesses its aerodynamic drag increases slowing the bullet thus shortening its range. In addition the point of the bullet will not hit first thus the bullet is deflected to some degree upon hitting its target.

3. NON-SPINNING - If the bullet doesn't spin as it flies, it only shoots straight and fast if it keeps its body exactly in line with the path of its flight. If its body goes out of line, due to a slight wobble as it leaves the barrel or anything else that might nudge the tip sideways, it tumbles end over end creating tremendous aerodynamic drag and an unpredictable flight path.

4. TOO MUCH SPIN - If bullets spin too fast, their jackets will heat up and you will increase the centrifugal force acting on the jacket, pulling it outward. The combination of heat, friction, and centrifugal force can cause jacket failure and the bullet will literally "blow-up".

5. RATE OF SPIN – Every rifled barrel that I am aware of gives bullets a clockwise spin. The rate of spin, RPM, is determined by the barrels length and barrel twist rate. Different bullets need different spin rates to perform optimally. Generally speaking, among bullets of the same caliber, longer bullets need more RPM to stabilize than do shorter bullets. Thus a short bullet would need a slow twist rate like 1:14 and a longer bullet a fast twist like 1:8.

**N.B.** A twist rate of 1:14 is SLOW because it imparts ONE rotation in 14 inches of bore travel. The twist rate of 1:8 is FAST because it imparts ONE full rotation in just 8 inches of bore travel.

With any rifling twist rate, the quicker the bullet passes through the rifling, the faster it will be spinning when it leaves the muzzle. To a certain extent, then, if you speed up the bullet, you can use a slower twist rate, and still end up with enough RPM to stabilize the bullet.

Let's calculate: Here is a simple formula for calculating bullet RPM:

MV(Muzzle Velocity) x (12/twist rate in inches) x 60 = Bullet RPM

Example One: In a 1:12 twist barrel the bullet will make one complete revolution for every 12″ (or 1 foot) it travels through the bore. With a bullet muzzle velocity of 3000 feet per second (FPS), in a 1:12″ twist barrel, the bullet will spin 3000 revolutions per SECOND (because it is traveling exactly one foot, and thereby making one complete revolution, in 1/3000 of a second). To convert to RPM, simply multiply by 60 since there are 60 seconds in a minute. Thus, at 3000 FPS, a bullet will be spinning at 3000 x 60, or 180,000 RPM, when it leaves the barrel.

Example Two: What about a faster twist rate, say a 1:8″ twist? Assuming the same MV of 3000 FPS, the bullet makes 12/8 or 1.5 revolutions for each 12″ or one foot it travels in the bore. Accordingly, the RPM is 3000 x (12/8) x 60, or 270,000 RPM.

6. Gyroscopic Stability Factor – Without going into the actual calculations, bullet stability can be quantified by the gyroscopic stability factor, SG. A bullet that is fired with inadequate spin will have an SG less than 1.0 and will tumble right out of the barrel. If you spin the bullet fast enough to achieve an SG of 1.5 or higher, it will fly point forward with accuracy and minimal drag.

Bullets flying with SGs between 1.0 and 1.5 are marginally stabilized and will fly with some amount of pitching and yawing. This induces extra drag, and reduces the bullets' effective BC (Ballistic Coefficient, a measure of its ability to overcome air resistance in flight. A high BC means the object will slow down less in flight (values for BC can be as low as 0.12 and as high as 1.00 for commonly used bullets). Bullets in this marginal stability condition can fly with good accuracy and precision, even though the BC is reduced. For short range applications, marginal stability isn't really an issue. However, to maximize performance at long range you need a twist rate that will fully stabilize the bullet, and produce an SG of 1.5 or higher.

7. TUMBLING WITHIN THE TARGET - Bullets are pointed at the front (called a spitzer). When the projectile strikes a body, the Newtonian law of inertia comes into play. The front or pointed end of the bullet since it weighs less than the back or base of the bullet, will slow down at a faster rate than does the heavier back or base of the bullet . This causes the bullet to yaw, a motion that some term "tumbling".
Certain bullets have what is called a cannelure, which is the crimping groove around the cylinder of the bullet. This is a weak point of the bullet and at high velocities this will rupture causing the bullet to fragment causing secondary wound channels.

Now let's consider the spin put on the bullet as it travels down the barrel of the weapon. You've got the order of events somewhat reversed. Once the stability of the bullet is upset by entering a body, these gyroscopic effects then further increase the yawing effect.
In non-military expanding bullets, if one side of the bullet becomes larger than the other side (usually caused by shedding actual small parts of the bullet) , this will then cause a bullet to go even further off line.

A good visuals of this are the YouTube videos by Brass Fletcher who has several high speed slow motion videos of bullets in clear ballistics gel.