Home Forums Hunting & Shooting Ask The Gunwriters Powder burn temperatures

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What you can use is barrel length to increase the accurate life of a barrel. A .308 with a 26" barrel is going to have a significantly longer barrel life than a 300 win mag cut to whatever length matches the velocity. You have less dwell time in the barrel in the 300 win mag, but a barrel will last way longer with a nominal 45 gr powder charge in the the .308 than a nominal 70 gr charge in the win mag.
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Not sure I am following this correctly. Are you saying to use a longer barrel to increase velocity instead of more powder? If this then yes but it sounds like you are saying longer barrels last longer?

I was making an example where you can achieve the same velocity with two different chamberings in the same caliber, and have one barrel shoot out much faster than the other. If you want a specific answer, you need to make a specific question.

How long a barrel will last basically comes down to how much powder you burn with each shot. The velocity you achieve has to factor in barrel length. For a given velocity (within reason) you can achieve longer barrel life by choosing a chambering that burns less powder and using a longer barrel.

There's a saying in racing that is perfectly applicable to this discussion. Speed costs money, how fast to you want to go?

Chemicals cause corrosive wear.

For the average rifle barrel, if you multiply the number of rounds doing down the barrel by the bullet dwell time in the barrel, the life of the barrel is six seconds.

I guess my question wasn't clear. There's a lot of answers to other questions, which I didn't intend on asking.

I have an 1898 Krag manufactured in 1899 (with an after market barrel). The accuracy is phenominal for about three shots. Then the accuracy goes Democrat, so to speak. I've shot this several times and the first shots with a cool barrel very good ~ 1 MOA or there abouts with selected loads. (IMR4350 170 grain 30-30 bullets)

My theory is that when the barrel heats the POI changes dramatically since depending on how fast I shoot, the latter shots can bring the group size to 12 MOA or there abouts.

I'm not worried about corrosion, erosion, etc. I do not plan on using this rifle as a bench rest rifle, but plan on hunting with it. I'm not going to shoot enough rounds through this rifle to wear it out. I suspect that I will eventually shoot only cast bullets in it, which I suspect will not heat the barrel nearly as fast as the jacketed loads. I was thinking about using a cast bullet approximately 200 grains and hollow point with the largest diameter bullet that will not interfere with chambering. Cast bullets, at least for me take quite a bit more trial and error than jacketed and I will do this in the next month or two, hopefully,

I feel that the way the barrel and the stock mate on a Krag isn't the best design for placing shots in the same location as the barrel heats.

I've now glass bedded the action and the fore-end tip. There now is a snug fitting front band. But this still is no Remington 700. I noticed that where the front action screw (front trigger screw) there was a gap bewteen the stock and the bottom of the action, which is now filled with glass.

I've not shot the rifle since glass bedding - too many projects.

Finally since this isn't a perfect gas, but is a chemical reaction I do not believe that pressure and heat created by the reaction to be linear with different powders, but I may be wrong.

My question was regarding to temperatures and powders.

Pretty much standard CONOPS on the 'fire is no matter what question you actually asked, us rifle loonies are likely to answer some tangential question we wish you'd asked, so we can wrestle with the trivia of rifle shooting.

Just a bit of trivia....I was using H4350 or something like that (slept since then!) in a 22-250 Ack Imp and 68gr Hornady OTM and the barrel got hot real fast. On a whim I tried N140. Sheboygin! Could shot a whole string before having to let it cool. BTW, that 68gr Hornady was an awesome bullet, I'd use it on deer in a heartbeat. As it was I just used it on coyotes and PDs.

Temperature in a compressed gas corresponds to pressure. That is simple physics.

The Hodgdons powder manuals list pressure with most of their load data. The loads listed with lower pressure will have lower temperature. What is not listed in the manual is peak pressure duration. The duration of peak temperature is just as conducive (or more so) to barrel heating (and flame erosion) as is peak temperature.

It is only simple physics if you are talking about a perfect gas and you are not talking about complex chemical reactions. In this case, this is not a perfect gas and it is a chemical reaction. There is a solid -powder- and a gas -oxygen. The chemical reaction started by athe primer causes the solid to become a gas. The gases created depend on the chemical make up of the solid. The amount of gas is dependent on the chemical make up of ingredients. In this case the change in ingredients is the powder, while oxygen is fairly constant. There are other variables, but unless I quickly move a couple thousand feet in elevation or a severe weather front comes through in the minute or two between shots, these other variable will not have an effect from shot to shot.

The pressure/temperature/volume laws apply whether the gas is ideal or not. The one that doesn't work with complex propellant gasses is PV=nRT. Propellants carry their own internal oxygen and do not depend on atmospheric oxygen.

The amount of gas produced is not linear with the temperatures produced. The other point that I’m making is there are other things that affect the temperature of combustion such as atmospheric conditions. In Spearfish SD the temperature changed from -30 to +40 degrees in 15 minutes. If firing during this period there would be other conditions that have affected the pressure and temperature of the firing of the cartridge. Normally these things can be considered constant as long as the temperature of things like the ammo is constant. Density of air, temperature of ammo etc.
When the ammo is hotter the the combustion is faster. The pressures increase due to the faster combustion. Yet the amount of gas produced is the same as long as there is complete combustion. The bullet will come out of the barrel faster due to the time the bullet is in the barrel there is higher pressure.

However the temperature and the pressure of two solids becoming gases are not linear. You are sticking with your thermo-dynamics story with how gases behave while ignoring the realities of the chemical properties of the different materials changing from solids to gases.

The amount of gas produced and the time it takes for complete combustion is different for different materials.

I am saying that powder “A” can produce the same velocity as powder “B” yet the temperature produced can be different all other things being equal.

The amount of gas produced is not linear with temp. The amount of gas produced is dependant upon propellant charge.

The pressure of that gas is linear with temperature.

Lots of external factors effect pressure/temp during ignition of a powder charge. The most important factor being barrel steel temperature. Compare the ignition cycle of the same rifle at two extrem temperatures. If a rifle is minus 100 degrees Celcius when it is fired, the barrel will suck many calories from the chemical reaction of the propellant, muzzle velocity will be reduced because heat was robbed from the reaction and lowered chamber pressure.

Compared to the same rifle fired at 200 degrees celcius. The barrel steel is three hundred degrees warmer, and while it is still much cooler than flame temperature of the powder charge, it will absorb much less heat from the reaction than the colder barrèl. Possibly allowing temperature and pressure to elevate far enough to become dangerous.

All of us have seen the variatons in muzzle velocity produced by shooting in varied temperatures. While we obviously do not shoot in the extreme conditions I portrayed, I have test fired rifles from minus 15 F to 110 degrees F. The differences in muzzle velocity are easily recorded and are solely dependant upon changes in chamber pressure.

If powder A produces the same velocity as powder B with powder A having a lower temperature, powder A also delivers a lower pressure. There are many examples of this., because the duration of powder B is longer.

Take for example the 30-06 with a 150 gr bullet. From Hodgdons #26, H322 at 46 gr will produce 2720 fps at 50700 cup. While H414 at 58 gr will produce 3043 fps at 48700 cup. H322 is the hotter of the two powders. It produced the highest temperature and highest chamber pressure. But H414 produces more gas because it uses more powder to start with. It produces more velocity at lower temperature because the pressure, although lower, is sustained over a greater period of time

Give or take some carbon residue and unburned powder, the mass of the gas equals the mass of the powder, just as Idaho Shooter said.

Smokeless powder converts almost entirely to propellant gas.

"Lots of external factors effect pressure/temp during ignition of a powder charge. The most important factor being barrel steel temperature. Compare the ignition cycle of the same rifle at two extrem temperatures. If a rifle is minus 100 degrees Celcius when it is fired, the barrel will suck many calories from the chemical reaction of the propellant, muzzle velocity will be reduced because heat was robbed from the reaction and lowered chamber pressure.

Compared to the same rifle fired at 200 degrees celcius. The barrel steel is three hundred degrees warmer, and while it is still much cooler than flame temperature of the powder charge, it will absorb much less heat from the reaction than the colder barrèl. Possibly allowing temperature and pressure to elevate far enough to become dangerous."

i'm neither physicist, ballistician nor engineer but, in your example of a barrel at -100 degrees or 200 degrees if the cartridge is room temperature when placed in the chamber and fired is there adequate time for barrel temperature to have a profound effect on gas pressure or volume ?

thanx

[quote=denton]

The Mass of the gas is one thing. The volume of gas is a whole different matter.

Of course.

Different topic......

A wrong idea that gets repeated over and over is that it's the initial temperature of the powder that affects muzzle velocity. Actually, it's just as was stated by Idaho Shooter: Cold steel robs more heat energy out of the gas than hot steel does. Ammunition temperature matters a little, but only because the brass and lead rob energy as well. Barrel temperature is about 3X as influential as brass and lead temperature.

Gas will expand to fill all space available, therefor volume (in the way you are using it) of gas is a non-relavant factor. Mass of the gas (more accurately, the number of gas molecules) times temperature devided by volume of containment vessel yields pressure.

This is why pressure and temp are linear.

As to barrel temp vs pressure: Denton has done the experiments and shown us the data. He knows that of which he speaks.

There’s three variables in the thermodynamic formula referred to as simple physics. This formula is valid in certain and certainly in what we’re discussing.
Pressure temperature and volume.

If volume is constant then a rise in temperature will subsequently cause a rise in pressure.
If volume is not held constant say absolute temperature is raised by ten percent and volume of gas in a confined space is also increased by ten percent, what is the resultant pressure?

Similarly if a solid sublimes or due to combustion creates gas, depending on the type of the gas produced, different amounts, in volume, of gas will be produced.

An extreme example. A frozen block 6 grams of hydrogen and a frozen block 6 grams of CO2 are thawed. The the gas produced will be 6 grams. Now if those gases are contained in one cubic meter, and the temperature is zero degrees C. The pressure inside the container of hydrogen will be greater than the container with CO2.

Now, consider the different chemical mixtures of powder.

I think you are making the problem more complicated than it really is. Let me try my hand at simplifying:

For any mixture of gasses, P1*V1/T1 = P2*V2/T2. Temperature has to be in Kelvins. This applies to the mix of CO2, N2, H2, etc. that is produced by propellants as well as it applies to a pure, ideal gas like Argon.

Now if you want to calculate pressure and temperature from volume, number of moles of gas, etc., the problem is as complicated as you think it is. But as long as you stick to the same mixture of gasses, you can fiddle with temperature, pressure, and volume using the formulas above. Fortunately, that's often enough.

That is the point! The same mixture of gasses or could I say the different mixture depending on the chemical make up of the powder. I don’t know if two powders that are the same, unless H110 and Win 296 or something such as that.