Barrel Life question.

[Djfergus]

Say we chamber two rifles in two different cartridges and barrel blanks are twins. One cartridge has 53 grains H2O capacity and the other has 66 grains H2O capacity. They are both 6.5mm cartridges and we load the exact same bullet in each at the same velocity with the same powder( let's say the powder is RL26). Both have the same shoulder angle and both have the same neck length and all other things being equal, which barrel wears out the fastest? I know more powder equates to less barrel life but I would also think that higher pressures of the smaller cartridge would also significantly contribute to less barrel life.

 

[jepp2]

which barrel wears out the fastest?

The one burning the greater amount of powder, provided the firing rate and maximum barrel temperature reached is no higher.

 

[CH87]

If it is the same bullet weight, same caliber, same velocity, wouldn’t the pressures then be the same? Just more powder in the larger case to create the same pressure due to extra volume. This is a good brain exercise.

 

[CH87]

If it is the same bullet weight, same caliber, same velocity, wouldn’t the pressures then be the same? Just more powder in the larger case to create the same pressure due to extra volume. This is a good brain exercise.

Or is less pressure required in the larger case because there is more volume of gas available once expanded to drive the bullet down the barrel. Hmmmmmm

 

[Djfergus]

I think the pressure curve in the barrel will be different. At some point the smaller cartridge will peak out with more pressure than the larger

 

[CH87]

I believe you are correct.

 

[Murray Brook]

I would think the the larger case would require less pressure to equal the velocity of the smaller case. With less pressure you would think that the barrel would last longer. If this makes any sense.

 

[wer0206]

Say we chamber two rifles in two different cartridges and barrel blanks are twins. One cartridge has 53 grains H2O capacity and the other has 66 grains H2O capacity. They are both 6.5mm cartridges and we load the exact same bullet in each at the same velocity with the same powder( let's say the powder is RL26). Both have the same shoulder angle and both have the same neck length and all other things being equal, which barrel wears out the fastest? I know more powder equates to less barrel life but I would also think that higher pressures of the smaller cartridge would also significantly contribute to less barrel life.

The Hornady guys have a shit ton of data on barrel life (see below video). In general what they found was if you shoot the same charge but down a smaller tube it will have the biggest impact on creating short barrel life. For example since a 6 creed is just a necked down 6.5 creed case, it will have a much shorter barrel life than a 6.5 creed. Same thing with 6.5 prc having a shorter life than a 7 prc etc.

They also found cases with 30 deg shoulders will create longer barrel life than a similar case with 20 degree shoulders due to the difference in how much powder is burning in the throat area vs the bore but this doesn’t have as much impact as powder burned to bore size ratio

 

[davidjoe]

I would analyze the question in terms of the barrels being like two different engines, required to produce the same power output, burning the same gasoline, where one is smaller displacement than the other.

All acted upon parts of the smaller displacement engine must experience greater pressure to accomplish the same amount of work.

Similarly a large and small hydraulic cylinder both capable of exerting X pounds of force will experience different internal pressure.

In gun terms this also bears out. We know that to get a .308 to shoot more like a 300 win mag, the .308 brass will be one and done. If the brass is short lived from the heightened pressure, that same pressure is certainly present for many inches into the bore.

 

[Djfergus]

It's my understanding that the most accuracy detrimental wear/erosion is fire cracking in the throat area. The cause of the fire cracking and eventual pieces breaking off is the amount and intensity of heat cycles. Saying all of that, the next question that I don't know the answer to: does increased pressure contribute to increased temperature of combustion in the throat area?

 

[jxb]

After so many years shooting both 220 Swift and 22-250 I loved seeing the numbers show that the Swift isn't the barrel burner so many think. Notice the numbers are actually better than the 22-250.

Of course there's other factors to consider like brass life is generally much better with the 22-250 but then the Swift's point blank range for a given target size is noticeably further so I view them as what tool for what task.

 

[Djfergus]

Here is some info that may have some relevance to my question:​

The relationship between pressure and temperature during combustion is governed by the principles of thermodynamics and the ideal gas law, which states:
PV=nRTPV=nRT
Where:

• PP is pressure,
• VV is volume,
• nn is the number of moles of gas,
• RR is the gas constant,
• TT is temperature.

If the same amount of fuel is combusted in a smaller displacement (volume), several things happen:

1. Higher Pressure in Smaller Volume:
   • The combustion process generates hot gases. In a smaller volume, these gases are compressed, resulting in higher pressure due to the limited space for expansion.
2. Temperature-Pressure Relationship:
   • According to the ideal gas law, at constant nn (moles of gas), reducing VV while increasing PP will increase TT (temperature). This means the temperature of the gases will rise as the pressure increases, assuming the system is insulated and no heat is lost to the surroundings.
3. Heat Generated:
   • The total heat energy released during combustion (dependent on the fuel's calorific value) remains the same because the amount of fuel remains constant. However, the temperature of the system can be higher in the smaller volume due to the increased pressure.

Key Insights:​

• Combustion in a smaller displacement produces higher pressure, which leads to a higher temperature of the gases, assuming ideal conditions with no heat loss.
• In a larger volume, the pressure and resulting temperature would be lower because the gases have more space to expand, reducing the energy density.

In real-world applications (e.g., engines), this principle is exploited in high-compression engines, where compressing the air-fuel mixture into a smaller space before combustion yields higher pressures and temperatures, improving efficiency and power output.

 

[davidjoe]

My thought is that heat and pressure are 97% of the cause of fire cracking.

I can envision using a reloading press to slowly ram bullets one at a time through the shank of a barrel for a couple of inches, doing that tens of thousands of times before all the rifling was gone. It would never fire crack, the grooves would just wear away ever so slowly.

Our bottleneck cartridges aren’t forcing the barrel to expand and spring back because the jacketed lead bullet is bigger than the bore, so much as because the pressure bubble pushing in all directions behind that bullet is probably 100 times greater than what is nominally required to merely get the bullet through the barrel, slowly. That pressure bubble stretches the bore then scalds the surface before it returns back to diameter.

The brevity of the torch effect may matter greatly as to how deep the heat sinks from one cycle, but the surface molecules do not need long exposure to sustain damage. I have seen high speed photos where flames emanate from the surface of a missile’s target before the circular supersonic blast of the explosion has even reached the object.

 

[jelenko]

Say we chamber two rifles in two different cartridges and barrel blanks are twins. One cartridge has 53 grains H2O capacity and the other has 66 grains H2O capacity. They are both 6.5mm cartridges and we load the exact same bullet in each at the same velocity with the same powder( let's say the powder is RL26). Both have the same shoulder angle and both have the same neck length and all other things being equal, which barrel wears out the fastest? I know more powder equates to less barrel life but I would also think that higher pressures of the smaller cartridge would also significantly contribute to less barrel life.

Given what you've specified, how do you know the smaller cartridge has higher pressures?

 

[Djfergus]

@jelenko If the smaller cartridge was pushed hard enough to show pressure signs and a given velocity was established, its likely that the larger cartridge would not show pressure signs at that same velocity.

 

[dgeesaman]

We know that seating a bullet short, which reduces case capacity, generates more pressure if all other things are held equal. (We are talking significantly shorter COAL here).

Therefore going from the larger to the smaller cartridge with everything else held equal should have the same effect.

Higher pressure = higher temperature = more aggressive barrel wear. But generally I would also expect better ignition and better performance.

 

[357Mag]

Say we chamber two rifles in two different cartridges and barrel blanks are twins. One cartridge has 53 grains H2O capacity and the other has 66 grains H2O capacity. They are both 6.5mm cartridges and we load the exact same bullet in each at the same velocity with the same powder( let's say the powder is RL26). Both have the same shoulder angle and both have the same neck length and all other things being equal, which barrel wears out the fastest? I know more powder equates to less barrel life but I would also think that higher pressures of the smaller cartridge would also significantly contribute to less barrel life.

DJF -

Howdy !

As renowned ballistician Homer Powley has told us…
“High pressure is hight temperature, and therefore, faster erosion, it is as simple as that”.

“ Expansion Ratio “:
Powley said that a rifle’s expansion ratio can tell you how efficient a certain rifle is at
“ converting chemical energy into kinetic energy “, by comparing it to other rifle’ expansion ratio(s).

Thinking out loud… IF all that is changed in the gun’s configuration is the chamber volume; that alone would change the rifle’s expansion ratio. The larger chamber capacity gun would have a lower expansion ratio ( however slight ) than the comparison rifle with the smaller chamber columns. Grossly “ overbore capacity “ rifles have comparatively low expansion ratios.

Given your postulated input conditions to the comparison exercise; you would ALSO be making an impact on both rifles expansion ratio by the use of differing powder charges.
I say that because the need for differing powder charge weights is implicitly implied by the statement saying “ …same bullet in each at the same velocity. “

Your testing therefore, would need to draw some correlation between case capacity and barrel erosion. Here again, expansion ratio ( ER ) comparison might be the best means ?
For purposes of running ER computations, one or both cases can be notional “ wildcats “.

As regards you input conditions statement “ …all other things being equal “; lease note:
When both cases use the same calibre, neck lg, shoulder angle, shoulder diam, and base diam; both cases would of necessity have to have different case lengths. That length difference ( under the remaining input conditions ) has to be exhibited; for the difference in case capacity you mentioned to be realized. I have no intent to be a smart _ _ _ ,
I’m “ just saying’ “.

Best of luck in you endeavor !


With regards,
357Mag

 

[mauser284]

The real question is "Why Bother?"?!?!?!

Since the advent of cheap acurate laser range finders and scopes that can be dialed quickly and easily with out removing scope caps faster and flatter does not matter any more!

Chasing velocity today is a fools folly and is not needed. On top of all of that we have the best bullet technology today ever between the controled expansion bullets like the Swift A-Frame and Nosler Partition and solid copper bullets velocity is almost a non-issue today as long as you choose a bullet that will expand and pentrate at the velocity your bullet will be going at the max range you plan to hunt at. This means you are not as directly tied to weight of the bullet as you once where with cup and core bullets so you can run a lighter than traditional bullet get more velocity and still have great penatration and expansion.

So in the past I would said that a 150gr. bullet is just stupid on 30/06 but if that 150gr bullet is a Barnes solid copper or a Nosler Partition that is different than a 150gr. Hornady ELDX which in my opinion detonates like a varmint bullet. Maybe you want to run a 130gr. solid copper or Partition in a 308 Win on deer.

This all assumes you reload and are not a slave to factory ammo and what they are willing to sell. The faster/flater game is really old obsolete thinking on most levels. If anything it reafrims why the older non-propritary, non-wildcats, non-magnums have stood the test of time and do not need to be replaced.

Learn to shoot! Learn to read the wind. Purchase an affordable laser range finder. Learn to dial!

 

[jelenko]

@jelenko If the smaller cartridge was pushed hard enough to show pressure signs and a given velocity was established, its likely that the larger cartridge would not show pressure signs at that same velocity.

If you loaded down the cartridge with more capacity so it had the same velocity as the smaller cartridge, would it be a safe load?

Also, could you say what the point or objective is of your original post?

 

[jelenko]

It's my understanding that the most accuracy detrimental wear/erosion is fire cracking in the throat area. The cause of the fire cracking and eventual pieces breaking off is the amount and intensity of heat cycles. Saying all of that, the next question that I don't know the answer to: does increased pressure contribute to increased temperature of combustion in the throat area?

You know the answer to that question from the universal gas law that you posted.