Chamber temperatures?

[jabilli]

Hey guys,

While playing in the forums here I came to wonder something:

Leading/bullet deformation is mostly caused by gas cutting... Which is the result of lead of the cast boolit being exposed to the extreme heat/pressure from firing. While figures for pressure are somewhat commonplace to find, I can't find (at least upon a quick search) information for how hot the chamber gasses are.

Why do I care to know this?
I'm tinkering with Zinc boolits...If not just Zinc I'm also interested in other materials. I do understand the melting temp of Lead to be somewhere in the ballpark of 625* F... and WW "lead" to be even lower (like 550ish)... Zinc melts at 780 or so. I'm wondering what kind of temperatures the boolits are exposed to, in hopes of being able to guess whether or not a boolit (of a given alloy/composition) will be prone to gas cutting or not.

Anyone know/have a source of info regarding this? Thanks!

[44man]

Heat on a boolit is such a short duration from powder it has no affect at all. Most heat will be from friction from the bore. Even a paper or card wad on a boolit base will not burn. I even find Dacron filler in front of the bench that did not melt.

[243winxb]

See post #20 here http://www.shootersforum.com/handloading-procedures-practices/82542-spherical-vs-extruded-powder.html Looks like a chart on powder temeratures. Not chamber temps. At least i think that is what it is. ??

[Bwana]

"Leading/bullet deformation is mostly caused by gas cutting..."

And to have gas cutting you must first have the gas passing by the boolit. This is why proper fit and a proper lube is important. The heat is secondary in the equation.

[williamwaco]

You will always have gas passing the bullet.

This happens with both cast and with jacketed bullets.

You can watch high speed videos and gas always exits the muzzle before the bullet.

When the base of the bullet exits the mouth of the case, and before the bullet enters and seals the bore, gas will pass the bullet.

[Bwana]

http://voices.yahoo.com/how-powder-erosion-effects-chamber-barrel-and-8511677.html

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA444069

The second one has pertinent data on page 2, figure 3.

[303Guy]

The gas leaking past a boolit (or bullet) has only one property - kinetic energy of each molecule or particle. That kinetic energy comes from temperature and pressure. That kinetic energy erodes material from the boolit. It does not erode copper jackets. Will it erode zinc? Less so than it would lead but how much less is a good question. Probably not that much less but soft alloy boolits don't gas cut as much as harder alloy boolits. That's because of obturation of softer alloy. So ironically, higher pressure loads might gas cut less than lower pressure loads.

Oh, gas cutting/gas erosion does occur with harder materials. Cordite for example has a high flame temperature and erodes the barrel steel. Although the pressure is not all that high the kinetic energy of the gas particles is very high due to the high temperature.

[Tatume]

You will always have gas passing the bullet. ... You can watch high speed videos and gas always exits the muzzle before the bullet.

The gas (air) in front of the bullet will also be expelled before the bullet exits the bore. Is this visually distinguishable from propellant gasses?

[runfiverun]

smoke is grey and cloudy,air [up here anyway] is clear.

if gas temp were that high you would anneal the cases with every shot.
and we wouldn't be buying torches and stuff to do that with.

[geargnasher]

You will always have gas passing the bullet.

This happens with both cast and with jacketed bullets.

You can watch high speed videos and gas always exits the muzzle before the bullet.

When the base of the bullet exits the mouth of the case, and before the bullet enters and seals the bore, gas will pass the bullet.

I don't know where you found an HS vid with a cast boolit, but I'd like to see it. I think I've watched every high-speed gun-related vid on utube and only found results from undersized jaxketed, which DO leak a lot. Also remember that the projectile is clearing the air and soot in the bore ahead of itself as it zips toward the muzzle, so there will be a little puff even if obturation is 100%.

Gear

[uscra112]

Do the Boyle's Law calculation for temperature/pressure/volume. I think you find that the momentary temperature of the gases is several thousand degrees. Emphasis on momentary - the time is so short that there isn't much heat transfer into the surrounding metal. Which is why the brass case doesn't melt. Gas that hot leaking past a boolit will tear it up, melting and vaporizing lead as it goes, however. Which is why we need a fluid sealant, also known as lube.

[Tatume]

smoke is grey and cloudy,air [up here anyway] is clear.

I don't recall that anybody said anything about smoke. The discussion was about propellant gasses. When air in front of a bullet is accelerated from zero to several thousand feet per second in one to three feet, significant compression occurs. Air that is compressed has a different density from ambient air. Therefore light that passes through it is diffracted, making a visible change. This is the reason you can see water, which is also clear.

[williamwaco]

I don't know where you found an HS vid with a cast boolit, but I'd like to see it. I think I've watched every high-speed gun-related vid on utube and only found results from undersized jaxketed, which DO leak a lot. Also remember that the projectile is clearing the air and soot in the bore ahead of itself as it zips toward the muzzle, so there will be a little puff even if obturation is 100%.

Gear


I have only seen one rifle video with a with a cast bullet. It was one of those 1,000,000 fps videos on Utube.
I will see if I can find the link.

.

[runfiverun]

yes the boolit does compress the air in the barell.
you get dieseling of many oils in the barell because of this.

[303Guy]

yes the boolit does compress the air in the barell.
you get dieseling of many oils in the barell because of this.Interesting comment. I've speculated on dieseling in the bore behind the bullet as being the cause of excess pressure with oily chamber, case or bore resulting in excess bolt face thrust which is being blamed on lack of case to chamber wall grip.

Anyway, there is a video - not on YouTube I think - of a 1911 being fired with cast and it clearly shows that puff of smoke in front of the boolit.