Thread: Is it Pressure or Powder Capacity?

Barrel erosion happens when gases bypass the bullet, this is a high-pressure high-temperature erosive FLOW. It's not enought there are hot gases present to erode the barrel that much. For example, shooting erosive Cordite .303 Mk VII ammo you can sometimes find that little wad thingy behind the bullet (see my avatar picture) as good as intact downrange.

I don't buy it that gases are significantly cooler 3-4 cm into the barrel, it's more that the bullet by then has found and married the lands and grooves and bypass of gases is less.

Originally Posted by Cordite

Barrel erosion happens when gases bypass the bullet, this is a high-pressure high-temperature erosive FLOW.

I don't buy it that gases are significantly cooler 3-4 cm into the barrel, it's more that the bullet by then has found and married the lands and grooves and bypass of gases is less.

Your post is difficult to understand, but I think you are saying that it is the pressure and temperature that causes barrel erosion not the amount of powder capacity of the cartridge.
I also have never heard the idea that erosion is caused when hot gases 'bypass' the bullet. I would have thought the greatest amount of gasses would be behind the bullet and hence be the main cause of erosion not the gasses in front of the bullet?

Originally Posted by Hermitage

Your post is difficult to understand, but I think you are saying that it is the pressure and temperature that causes barrel erosion not the amount of powder capacity of the cartridge.
I also have never heard the idea that erosion is caused when hot gases 'bypass' the bullet. I would have thought the greatest amount of gasses would be behind the bullet and hence be the main cause of erosion not the gasses in front of the bullet?

No it's not the momentary pressure nor the momentary heat, but the combination of these with FLOW. An imperfect seal causing gas leakage around a bullet damages both bullet and barrel.
- Gas behind gas sealing bullet flows at the speed of the bullet,
- Gas bypassing a bullet does so at massively high temp/pressure/velocity which maximises erosion.
- Gas once past and ahead of a bullet and moving towards the muzzle is a lower pressure/temp/velocity and negligible for barrel erosion.

Think of a giant holding a tungsten carbide file, and pressing it against a steel bar held in a vice. He presses it against the steel bar with a pressure of 40,000 pounds per square inch. The steel bar is getting slightly indented but no steel will be lost from the bar until he pushes the file forwards.

Likewise a momentary very hot gas at high pressure does little to erode the barrel unless it also FLOWS.

My illustration showing this difference is how my bullet wads are intact and unburnt after traveling down a barrel wedged between a known hot and erosive propellant and bullet. The gases do not move past the wads (which would destroy them near-instantly) but merely press against them.

An unobturated bullet will allow gas to bypass it at a massively high velocity (which will happen even more so in a wide throat). But when a bullet seals the rifling the gas can move no faster past the rifling than the speed of the bullet ahead of it.

From: https://chuckhawks.com/rifle_barrel.htm
"Barrel wear is due to erosion from the extreme heat and pressure caused by firing a cartridge. Erosion starts in the barrel's throat, where the rifling begins, as this is where the heat from the burning powder is greatest; it literally melts away the steel a tiny bit with every shot. Erosion gradually moves down the bore with use and can be seen with the naked eye as it becomes more severe. Heat is bad for barrels, so letting a barrel cool between shots extends barrel life.
As erosion occurs more powder gas blows past the bullet before it can seal the bore. This increases the rate of erosion and also lowers muzzle velocity. Falling velocity, compared to a new barrel, is a sign that a barrel is wearing out."

Originally Posted by zimmer

What accelerates the whole issue is strings of rapid shots ie heat.

Yeah, I took that as a given, but was more interested in powder capacity vs pressure rather than heat via rapid shooting (I don't rapid shoot my 25-06).