What happens to a gun barrel when over-heated due to continues firing?

Question

This question covers a machine gun to the gatling gun in the AC-130 gunship.

My impression was, an air-cooled barrel when over-heated render the gun in-operable, but dousing it with water will cool it down and make it fire accurately again. Why then not use a water-cooled (with anti-boil similar to a radiator) gun instead?

Answer 1

Its a question of accuracy. in that there is a relationship between bullet velocity and barrel erosion.

There was a time when throat erosion was talked about in rifles using the super-fast rounds. You will notice that some of the speeds of today's cartridges are almost unimaginable, and they seem to be getting faster. Has throat erosion or damage just become a thing of the past, or is it that no one really cares these days?

To answer your question you have to first ask what is the maximum speed at which a bullet can be launched where the rifling can no longer engrave the bullet and keep it spinning. Engraving the rifling is not the limit, at least not with current technologies. Depending on alloy, lead bullets skid down the barrel at around 2,000 feet per second (670mps), which is why the jacketed bullet was a parallel development required by the invention of smokeless powder. At velocities possible today, modern jacketed bullets will engrave into the lands and acquire the rifling spin.

The actual limitation is the propellants we use. Burning gases from nitrocellulose powders travel at about 5,300 fps, which is thus the theoretical velocity limit. The practical limit is somewhat lower since the gas must push the bullet down the bore and through the rifling, creating friction and reducing velocity. Very light bullets with limited bearing surface (less friction) can be pushed to very high velocities, possibly exceeding 5,000 fps if you believe some experimenters. But we all know light-for-caliber bullets lose velocity quickly, so the practical tradeoff is longer bullets (more friction) that cannot be pushed as fast but offer better downrange performance.

So the gattling gun used, has a smooth bore - smoothbore barrels with sabot rounds, as used in the most modern tank cannons--again, less friction and thus very high velocity. But the loss of superb accuracy, means that you can not be certain where the bullits will go, so you just pepper a large area.

Now, as to barrel wear, modern metallurgy and barrel coatings have indeed increased barrel life. The problem is that no two barrels are alike. None is perfectly smooth, and none is perfectly straight, nor is it of the exact same inner dimensions. So barrels wear at different rates. Continuing to shoot an overheated barrel--when the steel has become softer--accelerates wear.

the AC-130 can place 105mm, 40mm and 25mm munitions on target with first round accuracy. The GAU-12 25MM six-barrel gun pod firing rounds of 25 millimeter high explosive incendiary ammunition. because the barrels rotate, they have a chance to cool down enough between firing, to avoid overheating. the 1,800 rounds per minute, are divided between 7 barrels.

Answer 2

Okay, first of all, Gatling guns cannot overheat. Because of their design, each barrel fires a lot slower than the whole weapon and the high-speed rotation bleeds out a lot of heat.

And water-cooled machineguns were used in the past. They were abandonned because of weight and maintenance issues. Even properly blued and oiled, steel will rust when exposed to a lot of water. Also, to be truly effective, it would need a pump, some form of a heat exchanger and a lot of tubing. That would make it very impractical to carry in the field, to say the least. And it would waste valuable drinking water.

As for what happens to a machinegun barrel overheating from firing too much, I have a little anecdote from a buddy of mine. When he was still a tanker, he was tasked to see just how far he could push a light support weapon. So, something like 12 belts of ammunition were linked together and he started firing. After roughly 4 belts of continuous fire, he no longer needed to pull the trigger as the rounds were cooking off. At 6, the barrel was soft and was wobbling about, sending rounds still downrange but just about everywhere. At 8, he could see the rounds going through the transparent/white-hot metal. And not long thereafter it stopped functionning and had to be scrapped. The bolt assembly and carrier were fused, the barrel was welded onto the receiver and it would never be true again.

And if you ever cool down a barrel so brutally as to drop it in snow or empty right cold water on top of it, you can cause severe damage to the steel. A machinegun barrel isn't just a steel tube. It is a pretty adanced piece of technology, forged of very particular steel and treated in very specific ways in order to provide maximum performance.

Answer 3

When a weapon overheats, the barrel will warp, the breach gets hot and the weapon becomes unsafe to use, It can cause a 'premmy' a round in the breach discharging when the propellant becomes hot!..Water cooling a weapons such as a multi barrelled gun isnt feasible because of the amount of water required and the pressure pumps being to bulky and heavy for aircraft, Navy does use water, OTO Melara 76mm is a weapon in point, but they've got the room , and can carry the additional weight , the last field weapon to be exclusivly water cooled was i believe the old vickers .303 mk1 machine gun that dates back to 1915!..Hope thai helps you!

Answer 4

because man this one looks cooler. DAMN you ask a lot of questions.