barrel life
- Thread starter matthewpauls
- Start date
Depends on so many factor as to be impossible to answer quantitatively, however...
There is a more quantitative formula that helps narrow it down:
Case capacity in grains of H20 divided by the surface are of the case mouth. This yields an index number, and that number falls within a contunuum of barrel life.
For example: One of the longest lasting cartridges is the 30BR.
It has a case capacity of 38 grains of H20.
The 30 cal surface area is PiXR2 .154X.154 = 0.023716 X 3.1415= .074504
38/.07504 = 506 The 30 BR in a cut rifled barrel will last in excess of 8000 rounds, so... and index of 500 is really good.
The 6.5-284 has a documented accurate life of about 1000 accurate rounds
Case capacity = 66 grains H20 Case mouth area=.054738
Index = 1205
So... an index of 1200 is bad. An index of 500 is really good.
Here is where the cartridges you name fit in:
243 = 1164
22-250 = 1091
223 = 766
Therefore, with reasonable care, a 223 is likely good for as many as 5000 accurate rounds.
The 243 ~ 1300 - 1500 max
The 22-250 ~ 1500 - 2000 max
FYI, some other cartridges with poor barrel life:
7mm Rem Mag = Index 1326
220 Swift = Index 1218
25-06 = index 1273
Good barrel life:
308 = index 751
6BR = index 815
6.5 Grendel = index 639
There is a more quantitative formula that helps narrow it down:
Case capacity in grains of H20 divided by the surface are of the case mouth. This yields an index number, and that number falls within a contunuum of barrel life.
For example: One of the longest lasting cartridges is the 30BR.
It has a case capacity of 38 grains of H20.
The 30 cal surface area is PiXR2 .154X.154 = 0.023716 X 3.1415= .074504
38/.07504 = 506 The 30 BR in a cut rifled barrel will last in excess of 8000 rounds, so... and index of 500 is really good.
The 6.5-284 has a documented accurate life of about 1000 accurate rounds
Case capacity = 66 grains H20 Case mouth area=.054738
Index = 1205
So... an index of 1200 is bad. An index of 500 is really good.
Here is where the cartridges you name fit in:
243 = 1164
22-250 = 1091
223 = 766
Therefore, with reasonable care, a 223 is likely good for as many as 5000 accurate rounds.
The 243 ~ 1300 - 1500 max
The 22-250 ~ 1500 - 2000 max
FYI, some other cartridges with poor barrel life:
7mm Rem Mag = Index 1326
220 Swift = Index 1218
25-06 = index 1273
Good barrel life:
308 = index 751
6BR = index 815
6.5 Grendel = index 639
- Location
- Coquitlam, BC
What's everybody's experience with barrel life on a 6BR? Specifically a 1-8" shooting the heavies.
- Location
- Somewhere on the Hudson Bay Coast
Obtunded, that is the most logical attempt to classify barrel life that I've seen yet, I'm surprised I haven't come across it before. Ackley suggested that a powder charge a third of the bullet weight produced the best barrel life, but then said it didn't apply to .22 center fires which can do well with up to 32 grs or so. I think I would modify the formula slightly and use powder weight rather than the capacity of water, as barrel life can be effected by variations of the loads fired through it. As an extreme example consider the .375 Ultra, or for that matter any large capacity medium bore cartridge. The Ultra cartridge can be loaded with a 235 gr bullet backed by 107 grs of powder or with 84 grs backing a 380 gr bullet and the potential bore life at either extreme is not represented by the water capacity of the cartridge. If one was an ardent cast bullet shooter, a 300 gr bullet could be eased out of the barrel with 16 grs of Unique!
rishu_pepper, going by Obtunded formula, the 6BR index is approximately 94% of the .223's, so if we take the 5000 round life of the .223 literally, then the barrel life of the 6 BR would about 4700 rounds. If you used heavy for caliber bullets exclusively, I believe that would result in slightly better barrel life due to the decreased powder charge, all things being equal.
rishu_pepper, going by Obtunded formula, the 6BR index is approximately 94% of the .223's, so if we take the 5000 round life of the .223 literally, then the barrel life of the 6 BR would about 4700 rounds. If you used heavy for caliber bullets exclusively, I believe that would result in slightly better barrel life due to the decreased powder charge, all things being equal.
Well done - of course it will be picked apart at its edges (someone always must), but that's a good scientific approach.
For the simpler mind, a simple rule of thumb would be "large powder capacity and small bore size results in lower accurate barrel life", and vice-versa, right? The high wear in high "index" cartridges comes from the abrasive effect of lots of powder being forced down a small tube, and it seems that most wear would occur closest to the case mouth where the temperature and pressure are highest and where some of the powder is still unburned (and more abrasive). I also imagine that spherical powder would be less abrasive than extruded, and experience seems to prove that out.
For the simpler mind, a simple rule of thumb would be "large powder capacity and small bore size results in lower accurate barrel life", and vice-versa, right? The high wear in high "index" cartridges comes from the abrasive effect of lots of powder being forced down a small tube, and it seems that most wear would occur closest to the case mouth where the temperature and pressure are highest and where some of the powder is still unburned (and more abrasive). I also imagine that spherical powder would be less abrasive than extruded, and experience seems to prove that out.
Even for the same caliber, it really depends on the load. A load consisting of a light bullet being bushed really fast with a large charge of powder will burn out a barrel quicker than a load consisting of a heavy bullet being pushed at a lower speed with a lower volume of powders. Coatings like moly and hBN reduce wear and extend barrel life.
All other things being equal:
Higher velocity = less barrel life
Larger powder charge = less barrel life
Higher pressure = less barrel life
Bullet coatings = more barrel life
Here is a calculator that estimates barrel life:
http://accurateshooter.wordpress.com/2008/10/21/spreadsheet-formula-calculates-useful-barrel-life/
All other things being equal:
Higher velocity = less barrel life
Larger powder charge = less barrel life
Higher pressure = less barrel life
Bullet coatings = more barrel life
Here is a calculator that estimates barrel life:
http://accurateshooter.wordpress.com/2008/10/21/spreadsheet-formula-calculates-useful-barrel-life/
The formula is not perfect for sure and there are many variables to throw in the mix. For instance, the single biggest destroyer of throats is over-heating. A 30 BR fired like a belt fed machine gun is not going to last 8000 rounds. Also, the formula does not take into account they variable in terms of powder charges and bullet weights. Lastly, the number it produces is an index, not an absolute figure.
The 6BR is indeed good for about 4000 rounds IF IT IS FIRED SLOWLY AND NOT OVER-HEATED. the majority however, are not. 2000 - 2500 is a typical accurate life.
The 50 BMG has an index in excess if 1400, yet it has a reasonable barrel life, likely because few can tolerate or afford to lob a bet of ammo down range in one sitting. I think this formula has flaws with large diameter bores to be honest. A "bore factor" needs to be added me thinks.
Also, this formula represents "functional accuracy". I am convinced that the most accurate life of ANY barrel is in its first 200-500 rounds. After that, a degredation in accuracy occurs that may be very slight in some, or substantial in others, but it does happen. The formula really represents what i would arguable call "F-Class Accuracy", that is, sub . 5 moa accuracy (I'm using a custom barrel as a term of reference, as many factory barrels are incapable of this accuracy even when new) . Many old 6.5X55 rifles have thousands of rounds down them and are still more than accurate enough to hunt with. Accuracy and barrel life are relative to purpose and expectation.
Kombayotch: I agree with everything except bullet coatings. There is a distinct lack of objective credible research out there to support that. Also, the benefits are often offset by the need for more powder to maintain an equal velocity.
The 6BR is indeed good for about 4000 rounds IF IT IS FIRED SLOWLY AND NOT OVER-HEATED. the majority however, are not. 2000 - 2500 is a typical accurate life.
The 50 BMG has an index in excess if 1400, yet it has a reasonable barrel life, likely because few can tolerate or afford to lob a bet of ammo down range in one sitting. I think this formula has flaws with large diameter bores to be honest. A "bore factor" needs to be added me thinks.
Also, this formula represents "functional accuracy". I am convinced that the most accurate life of ANY barrel is in its first 200-500 rounds. After that, a degredation in accuracy occurs that may be very slight in some, or substantial in others, but it does happen. The formula really represents what i would arguable call "F-Class Accuracy", that is, sub . 5 moa accuracy (I'm using a custom barrel as a term of reference, as many factory barrels are incapable of this accuracy even when new) . Many old 6.5X55 rifles have thousands of rounds down them and are still more than accurate enough to hunt with. Accuracy and barrel life are relative to purpose and expectation.
Kombayotch: I agree with everything except bullet coatings. There is a distinct lack of objective credible research out there to support that. Also, the benefits are often offset by the need for more powder to maintain an equal velocity.
I am interested in knowing when a barrel has reached the end of it's acurate life.
Are there visual clues, measurements and grouping trends that one can look for.
Especially important when claims of "only fired 4 boxes of shells" and the like are made.
Are there visual clues, measurements and grouping trends that one can look for.
Especially important when claims of "only fired 4 boxes of shells" and the like are made.
- Location
- Somewhere on the Hudson Bay Coast
When the rifle will no longer do what you need it to, its life is over. That of course is end use specific. A quarter minute bench gun will not live to see a round count as high as a rifle needed to put a moose in the freezer. Visual clues might include an increase in fouling at the throat, or if you have a bore scope you might see deterioration of the throat. Careful measurment of the lead over time will show the wear the throat suffers, you might be able to chase the throat to extend the barrel life, first by seating the bullet longer then by shortening the barrel, rechambering and rethreading, but from what I understand this practice is no longer cost effective.
actually the reading i have found on this subject seemd to point to the opposite. the reasoning is that the barrel is exposed to the high pressures for a longer period of time ( relative to the lighter weight). has anyone else read or heard this?
- Location
- Somewhere on the Hudson Bay Coast
Generally the maximum pressure for any given cartridge is irrespective of bullet weight. For example a .308 can be safely loaded to the same pressure with 110 gr bullets or with 220 gr bullets, thus there is no difference with respect to pressure. However, the hotter the flame from the propellant gases, and the longer the duration of the burn do effect throat erosion.
I don't believe that it does anything to slow throat erosion, but it should reduce heat and wear due to friction further down the bore.
"I am interested in knowing when a barrel has reached the end of it's acurate life.
Are there visual clues, measurements and grouping trends that one can look for."
One thing to consider is the difference between stainless steel barrels and blue barrels.
A blue barrel erodes gradually in the throat. You can see and measure the throat getting deeper and the rifling getting shallower. Accuracy gradually falls off. A blue barrel in 308 lasts 2,000-3000 rounds.
In stainless the erosion is in the form of cracks. With a bore scope the throat looks like the cracks in dried mud. They get longer and deeper, but accuracy holds up until one day a piece of steel between two cracks flakes off, and accuracy drops big time. In 308, the barrel life is about double that of a blue barrel.
YMMV
Are there visual clues, measurements and grouping trends that one can look for."
One thing to consider is the difference between stainless steel barrels and blue barrels.
A blue barrel erodes gradually in the throat. You can see and measure the throat getting deeper and the rifling getting shallower. Accuracy gradually falls off. A blue barrel in 308 lasts 2,000-3000 rounds.
In stainless the erosion is in the form of cracks. With a bore scope the throat looks like the cracks in dried mud. They get longer and deeper, but accuracy holds up until one day a piece of steel between two cracks flakes off, and accuracy drops big time. In 308, the barrel life is about double that of a blue barrel.
YMMV
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Can you define "reasonable life" for the 50BMG? I was wondering about this a while ago and meant to ask here. Not that I plan to buy one and shoot 1000+ rounds per year or anything, just curious how the big 50 stacks up against more typical rifle calibres.
Mark
