Home Forums Hunting & Shooting Ask The Gunwriters What creates barrel heat: velocity or pressure?

I agree that the burning powder contributes most of the heat, but friction does contribute something (even a little) - just clasp you hands together tightly and rub them together fast. Even rubbing once will generate some surface heat that adds to the barrel temperature.

the copper of the bullet will absorb more heat from friction than the barrel steel. but all that is of such a low value, its the hot gas that produces barrel heat, pressure is the resistance to flow of the hot gas produced by burning the powder.

How hot does an air rifle get from friction heat?

Interesting question!

Different ball park, different league, different game �

Compressed air cools when it's suddenly released and expands.

May have something to do with why quality air-rifle barrels are bronze or brass, not steel!

Something to scratch the ol' noggin about, isn't it?

Next question � Does that cooling absorb the heat of the pellet-barrel friction?

I'll never tell!

So, to apply this to a real scenario:

If I load a 22-250 and a 223 to 3200fps, the 22-250 will actually create less heat since it took a lower pressure to accomplish the same velocity?

PS--I have a vague recollection (sorry Ken) of a 220 Howell developed with the same principle in mind.

Well, it has been 30 years (!) since I had thermo class, but I recall convective heat transfer implies the motion of the gases is contributing to the transfer; the greater the churning (velocity) of the fluid, the greater the heat transfer. Conductive heat transfer is usually between metals in contact.

I believe convective heat transfer will be most of it. The molecules in the gas are incredibly energetic, and with the motion of the fluid, each molecule that dumps energy into the barrel is soon whisked aside by another fresh, hot molecule in the stream.

It's been a while since I read John Corner's book on internal ballistics, but I recall radiative transfer is about 1/4 of the total. The QuickLoad manual might include an estimate.

edit I'll quote the Wikipedia: Although often discussed as a third method of heat transfer, convective heat transfer actually describes the combined effects of conduction and fluid flow.

Fair enough.

An eloquent answer.



Not so.

If two otherwise identical objects are at the same temperature, and one has twice as much mass as the other, the one with the greater mass has twice the thermal energy.

The mass of the gas after combustion equals the mass of the powder before combustion. The 22-250 has a considerably larger mass of powder, hence more heat energy, all other factors equal.

Anybody who's shot various .22 caliber centerfires extensively should have noticed that sporter-weight barrels of:

1) A .22 Hornet firing a 40-grain bullet at 3000 fps...

2) A .221 Fireball shooting a 50-grain bullet at 3000 fps...

3) A .223 Remington shooting a 55-grain bullet at 3100 fps...

...will heat up at VERY different rates.

The friction of the bullets is a factor, since they have different bearing surfaces. But the big heat factor is the amount of powder being burned.

I know I've been burned by a piece of brass thrown out of rifle and that weren't because of the friction caused by it being tossed.

It seemed to me that so much heat transferred from a gas over milliseconds would be rather remarkable. Then the light bulb went on, the gas is quite dense at peak pressure. Don't discount conduction. Would be interesting to measure the temperature along a non-tapered barrel.

Yep. Amazing how hot a brass case is when jerked out before the heat can be transferred to the chamber. And there ain't no bullet friction involved.

I was going to do that with several cartridges, but first the great expense and then a stroke blew that plan all to Hell (and a few more hospital "vacations" followed).

I forget, now, where I was going to get the stick-on sensors and the recording software. I remember vividly that the cost made me gasp but don't remember the $$ range.

So I'm still curious. Had a bunch of intriguing and practical heat studies planned.

So Ken and all,

Shooting the same bullet.

Will a cartridge case holding 60 grains of slow powder (RS Magnum) at 50,00 psi have a longer barrel life
than the same case burning 50 grains of a moderate faster powder (RS Hunter) at 60,000 psi?

10 grains more 10,000 less psi
10 grains less 10,000 more psi

Which one will produce more heat?

Now we get to the question of whether by "heat" we're talking about Btu or �F or both.

A pine log shredded into excelsior and a kitchen match burn at about the same �F, but the excelsior produces a heck of a lot more Btu.

Light and heavy powder charges burning at different rates in vastly different combustion enclosures are hard to compare � impossible to compare simply. Intuition and country-boy logic offer no help at all.

If I win the lottery �

Ok, so back to my question. How about the same enclosure?

Funny, interesting, whatever...

I have been asking this question here at the campfire probably once a year and still no answer.

That's why I get the brass out of the chamber as quickly as possible. I don't know how much it really helps keep the barrel cool, but I feel better about it.

Lower peak pressure means longer barrel life � as I've explained here repeatedly, ad nauseam, for several years.

The larger charge produces more Btu than the smaller charge � at the lower peak pressure, the peak �F is lower than the temperature at the higher pressure.

Load a .30-06 to .30-30 or .30-40 maximum peak pressure, and your barrel will be accurate longer.

To intuit the significant difference between �F and Btu, heat a room now with propane, later with pi�on. The gas will have to be hot (�F) to put-out any Btu, and the pi�on will put-out a lot of cozy Btu at a much lower �F.

My grandparents in south Alabama used to "heat" each occupied room with butane. You'd have to huddle over the heater to keep your front warm while your back side turned blue. One night, I was leaning back in my chair, just barely warm enough to be comfortable, with my feet toward the gas heater. One boot caught fire. Out in the center of the room, you could see your breath. Lots of �F, not many Btu, rapid dissipation.

adiabatic heat pump according to Art Alphin's manual

I don't have any idea what it means

adiabatic � occurring without gain or loss of heat