Barrel Life

[Edd]

Which 6.5 barrel will have the longest life?

One of them uses 40 gr of powder and has 60,000 psi.
One of them uses 50 gr of powder and has 50,000 psi.

The muzzle velocity is the same and they both use the same bullet.

 

[BallisticsGuy]

Easy to calculate to an approximation (this is calculating match barrel life and I've found the equations to turn out very reliable data up to .30cal bore diameter) but I think you'll be surprised at the result. I choose H4350 for the powder.

50gr @ 50000psi 1507
40gr @ 60000psi 1920
50gr @ 60000psi 1256
40gr @ 50000psi 2355

 

[Edd]

Easy to calculate to an approximation (this is calculating match barrel life and I've found the equations to turn out very reliable data up to .30cal bore diameter) but I think you'll be surprised at the result. I choose H4350 for the powder.

50gr @ 50000psi 1507
40gr @ 60000psi 1920
50gr @ 60000psi 1256
40gr @ 50000psi 2355

What is the life when using H1000 for the 50 gr @ 50,000 psi?

 

[mindcrime]

Easy to calculate to an approximation (this is calculating match barrel life and I've found the equations to turn out very reliable data up to .30cal bore diameter) but I think you'll be surprised at the result. I choose H4350 for the powder.

50gr @ 50000psi 1507
40gr @ 60000psi 1920
50gr @ 60000psi 1256
40gr @ 50000psi 2355

If one thinks of unburnt powder as sand blasting media (which in a way, it is!); the LESS powder in a cartridge, with the bore size the same, the barrel and throat life should be better!!!

 

[ntsqd]

My recent experience in disposing of old powder given to me (differences in how far I had to step back out of the heat) leads me to think that the lower the BTU content of the powder the more favorable to barrel life it will be.

If the above .30-378 example could launch those those two bullet weights to those velocities with the same charge of the same powder, then I'd agree with the concept. As soon as one bullet needs a different powder or a different charge weight, or both, the bet is off.

 

[BallisticsGuy]

What is the life when using H1000 for the 50 gr @ 50,000 psi?

First, these are not hard and fast numbers so don't get too caught up in them. They're best used as a rough approximation. Like I've said before, the numbers have shown to be remarkably accurate in my long term testing at determining when a pipe would start to fail to hold match grade performance enough that I notice in competition.

Second, 2418rds. Bump the pressure to 60k and it goes down to 2015rds.

 

[BallisticsGuy]

If one thinks of unburnt powder as sand blasting media (which in a way, it is!); the LESS powder in a cartridge, with the bore size the same, the barrel and throat life should be better!!!

Yes but that's making a huge assumption about the mechanical erosion component's contribution, for which no useful study data exists that I know of and, mechanical erosion by powder would not be the only erosion mechanism of note. The high temperature gasses literally vaporize a bit of steel on each shot. Pressure and powder volume are equal enemies. High pressures convert directly to high temperatures.

If you want better throat life, then keep pressures low, use the least mass of powder possible, keep your shoulder angle + neck length set up so that the flame intersection point is inside the case neck and of course don't shoot with the barrel hot.

 

[L.Sherm]

Second, 2418rds. Bump the pressure to 60k and it goes down to 2015rds

99.9 % of us have no way of knowing how much psi were running whether its 50, 60 or 70. Only thing you have to go off of is books that tell you x cal. With y charge gives you z pressure. I know barrels, reamers and other things influence pressure.

 

[Buster Hemlock]

Which 6.5 barrel will have the longest life?

One of them uses 40 gr of powder and has 60,000 psi.
One of them uses 50 gr of powder and has 50,000 psi.

The muzzle velocity is the same and they both use the same bullet.

Check out this article and the excel sheet that is linked and you can do some tinkering of your own.
https://www.accurateshooter.com/technical-articles/excel-formula-predicts-useful-barrel-life/

 

[esshup]

If you want better throat life, then keep pressures low, use the least mass of powder possible, keep your shoulder angle + neck length set up so that the flame intersection point is inside the case neck and of course don't shoot with the barrel hot.

I bet the heat of the barrel has more to do with how fast it erodes than any other part of the equation. If I were to shoot 1 shot every hour for 2000 rounds vs. shooting the gun enough so you'd cook your hand on the barrel, I'd bet the barrel will have a much shorter life with the hot barrel. I was told not to shoot and let the barrel cool off if I couldn't rest my hand on the barrel in front of the scope.

 

[BallisticsGuy]

Nope. Not at all in fact on the first assertion. Your second assertion is basically correct but not for the reasons you think.

You have to think in terms of continuously interacting factors, not in an only-cause/only-effect way because you're dealing with a positive feedback loop but one that's interruptible and is usually interrupted. Positive feedback loops are very powerful as long as they're continuously engaged. Disengaging them though has a way of lessening the drama of their potential power.

The increase in barrel temperature is the PRODUCT of all the things that cause the wear. Not literally the cause. In fact, I could wear out a barrel without ever letting it get over 0deg C and it wouldn't take dramatically longer than wearing one out by never letting it get over 30C but cross into 50C+ and you start seeing results in much shorter time slices.

Barrel heat getting painful to the touch is telling you about how much abuse you've already carried out in the current shooting session and has no real effect on the next shooting session other than you starting off with possibly more or less wear than you might otherwise have.

 

[esshup]

Nope. Not at all in fact on the first assertion. Your second assertion is basically correct but not for the reasons you think.

You have to think in terms of continuously interacting factors, not in an only-cause/only-effect way because you're dealing with a positive feedback loop but one that's interruptible and is usually interrupted. Positive feedback loops are very powerful as long as they're continuously engaged. Disengaging them though has a way of lessening the drama of their potential power.

The increase in barrel temperature is the PRODUCT of all the things that cause the wear. Not literally the cause. In fact, I could wear out a barrel without ever letting it get over 0deg C and it wouldn't take dramatically longer than wearing one out by never letting it get over 30C but cross into 50C+ and you start seeing results in much shorter time slices.

Barrel heat getting painful to the touch is telling you about how much abuse you've already carried out in the current shooting session and has no real effect on the next shooting session other than you starting off with possibly more or less wear than you might otherwise have.

If I understand that correctly, I'll agree to that. If the barrel is too hot to comfortably rest your hand on it, the damage for that shooting session is already done. Do that multiple times and the life is shortened considerably faster than if the temp was kept below 30°C. I have no way of testing it, but I believe that the bore temp is much greater than the temp on the outside of the barrel.

Does barrel contour/heat dissipating qualities of the barrel design, help prolong barrel life? All other factors unchanged, except how fast the barrel will dissipate heat.

 

[Rflshootr]

What I was taught many years ago is pretty simple, and it makes sense...at least to me....a barrel will only burn so many grains of powder. Whether you choose to shoot a lot of grains each shot or a moderate amount of grains on each shot, you're still only going to burn a certain amount of powder before the barrel is worn out. Myself, I'm in it for the fun and when a barrel is toast, it gets replaced and the old one becomes a fancy, expensive tomato stake.

 

[Mikecr]

I wrote the spreadsheet linked to. That's a very old version with bugs. Asked the site to remove it, but apparently they can't... I have a way better version available.

An important distinction with barrel life estimates is that we're talking ACCURATE barrel life. Otherwise, barrels pretty much last forever.
By far most shooters never know their accurate barrel lives, because they never reached a peak accuracy to begin with. They just accept what they have as good enough. And if good enough was ~1moa, then hell most barrels will go 2-3 accurate barrel lives before breaking that.. Where good enough is usually 1/4moa or less, then these folks will know right to the session/relay when their barrel dies. It's actually a step change.

The inexperienced and stubborn will chase their tails to regain accuracy. More development, barrel setbacks, etc. But eventually they'll learn that they should have anticipated a barrel dying, with a new barrel ready & waiting. It saves so much effort and money with this.