Bore Capacity versus Barrel Life

[mgood]

How does this fit in with Gunworks and their 6.5 using H1000 and supposedly getting over 2000 in barrel life. The Sherman and SS, seem to be reporting the same longer life than shown by this chart. What is different?

The fairly steep shoulder and longer neck of the Sherman and SS cartridges may focus the hottest part of the flame inside the case neck rather than on the start of the rifling. This should increase barrel life, at least I think that was the theory, and I think it makes sense. How much it may affect barrel life, I have no clue.

 

[DocDoc]

That was the point of my question. From the results is the Sherman, SS, RSAUM, and others, it looks like neck length, case design, heavy for caliber bullets, slow powders, and rational pressure can greatly extend barrel life.

 

[Mikecr]

Ok, answer me this. 6.5 RSAUM running 61.5 grs H1000 59K still 1/2 moa after 3000 rounds or how about factory 7MM STW that ran hot loads 88 grs H1000 65-70K for the first 1000 rounds approximately and then another almost 500 rounds of 60-65K before the barrel puked. 6.5 has Bartlein bbl and STW a factory cryoed bbl.

Half the trick here is H1000, which is among the coolest of all powders.
The other half is a gun that will still shoot 1/2moa -even well beyond it's best accuracy(which was better than 1/2moa).
Not everyone can do so well with their guns and cartridges and H1000. That's why I call it a trick (an anomaly) rather than a standard of reference.
Remember, when talking anomalies, 1/2moa sucks.

Complicating the measure more are the differences between 'accuracy' and 'precision'.
When we suggest a gun is still a 1/2moa shooter, we're not qualifying this as accuracy, or precision, or both. Most shooters do not even know the difference.

6PPC shooters use N133, which is as cool as H1000 only way faster burning. But to be competitive these shooters must reach for extreme pressures, viable only in such a tiny cartridge, and their shot rate is very fast (tied to favorable conditions). With this, their fortunate to keep a barrel shooting at it's best potential(competitive) beyond 1,000 rounds. Most replace by then.
Now any of us could make that tossed barrel last thousands more and still shoot 1/2moa accurate, or maybe even 1/2moa precision.
So what is the 'accurate barrel life' of a 6PPC? It depends on your use and your measure.

This is LRH here. We should concern ourselves with accuracy(POI from mark), and a well shot out barrel might still be accurate enough for single cold bore shots (or not).
Problem is, nobody is measuring 'cold bore accurate barrel life'. Most are not measuring accuracy at all.
The only standard of measure available for us to see is precision(grouping). It's just what we measure, and it certainly takes barrels to their point of opening precision. THIS can be a reference for accurate barrel life, even if a misnomer.

If you take a GAP 6.5saum/61.5 H1000/59Kpsi and group shoot with it from the beginning, it will shoot awesome 1/4-3/8moa groups for about ~1300 rounds (a little better than the 6.5-284). This, with ~45sec shot rate and we're talking GAP now,, a very well built gun.
At this point, well, very near this point, the grouping will open a bit -like a switch thrown. By 3,000 rounds you can still pull off 1/2moa grouping with it, about half the time. So many would suggest it's accurate barrel life just keeps going and going..
No, it's accurate barrel life with that use & load was ~1300 rounds, and you passed it.
The only known way to extend that -today- is melonite treatment of the bore.

 

[TOM H]

Been lot of articles on barrel life from (Homer) Powley which is mentioned in Ackley book to this one.


"Overbore" Cartridges Defined by Formula within AccurateShooter.com

I'm not trying to take anything away from Bart data but this is his 2nd try at it.

 

[DocDoc]

Mikecr, are you willing to share your App, so others can look at how powder ect, changes life expectancy?

 

[Greyfox]

Tagging on.....interesting info!!!!

 

[Barrelnut]

Mikecr, are you willing to share your App, so others can look at how powder ect, changes life expectancy?

I believe it is still the same one from Mike's article here.
Excel Formula Predicts Useful Barrel Life within AccurateShooter.com

 

[Rich Coyle]

Melonite has been mentioned a couple times. How does one apply it? How does it compare with salt bath nitride? Can they be used together?

 

[Bart B]

In spite of TOM H's ongoing vendetta of bad mouthing most everything I post, I applaud his posting the link to different formulas including Mikecr's software. That was a good idea. Mike used my powder grains and bore area base, then improved it by adding powder heat indexes. I don't know the exact data base for cartridge barrel lifes Mike used developing his formula. I mostly used Sierra Bullets' data as their test barrels were in rail guns shot indoors at 100 yards at their California plant with 10-shot control groups opening up 50% from when the barrel was new. Sierra's tests were indoors with a very stable atmosphere and eliminated all human and rifle variables. Their data showed a gradual loss of accuracy throughout the barrel life for most cartridges. About one-fifth of my data base came from competitive shooters testing match rifles clamped in machine rests outdoors.

Comparing results between my old formula and Mike's using the same powder for a given cartridge, his gives about 20% average more round counts than mine. Partly because there are more cooler and better powders these days in the burn rates best for accuracy.

That formula in a link using bore area divided by case capacity (grains of water) to get a ratio is close to my first formula tried. I calculated the volume in cubic inches (very tedious) divided by the actual area of that hole in the barrel (SAAMI spec for minimum bore plus groove area; example, 0736 sq. in. for most 30 caliber barrels) which is about mid point between using bore diameter or groove diameter. That got too much figuring so I simplified the formula to get an approximate barrel life to show how it changes for a given caliber.

Of course, none of these formulas are exact, but they do show how barrel lives change with charge choice and weight for a given cartridge. Use your own objectives, conditions and standards then shoot your ammo until it starts missing your point of aim too far.

 

[Bart B]

Ok, answer me this. 6.5 RSAUM running 61.5 grs H1000 59K still 1/2 moa after 3000 rounds or how about factory 7MM STW that ran hot loads 88 grs H1000 65-70K for the first 1000 rounds approximately and then another almost 500 rounds of 60-65K before the barrel puked. 6.5 has Bartlein bbl and STW a factory cryoed bbl.

As I don't know the details of your tests to get the 1/2" size, I cannot speculate why you get those barrel life results. Is that half inch an average, smallest, biggest, mean radius...? How many shots per group? How was the rifle aimed? What group size is your limit when it pukes?

I don't think any center fire barrel will consistently shoot any group size for one nor two thousand rounds. They tend to slowly loose accuracy. Rim fire barrels used by winners get replaced at 30 to 40 thousand rounds.

Whose transducer psi system did you use to get those pressure numbers?

 

[TOM H]

In spite of TOM H's ongoing vendetta of bad mouthing most everything I post, I applaud his posting the link to different formulas including Mikecr's software. That was a good idea. Mike used my powder grains and bore area base, then improved it by adding powder heat indexes. I don't know the exact data base for cartridge barrel lifes Mike used developing his formula. I mostly used Sierra Bullets' data as their test barrels were in rail guns shot indoors at 100 yards at their California plant with 10-shot control groups opening up 50% from when the barrel was new. Sierra's tests were indoors with a very stable atmosphere and eliminated all human and rifle variables. Their data showed a gradual loss of accuracy throughout the barrel life for most cartridges. About one-fifth of my data base came from competitive shooters testing match rifles clamped in machine rests outdoors.

Comparing results between my old formula and Mike's using the same powder for a given cartridge, his gives about 20% average more round counts than mine. Partly because there are more cooler and better powders these days in the burn rates best for accuracy.

That formula in a link using bore area divided by case capacity (grains of water) to get a ratio is close to my first formula tried. I calculated the volume in cubic inches (very tedious) divided by the actual area of that hole in the barrel (SAAMI spec for minimum bore plus groove area; example, 0736 sq. in. for most 30 caliber barrels) which is about mid point between using bore diameter or groove diameter. That got too much figuring so I simplified the formula to get an approximate barrel life to show how it changes for a given caliber.

Of course, none of these formulas are exact, but they do show how barrel lives change with charge choice and weight for a given cartridge. Use your own objectives, conditions and standards then shoot your ammo until it starts missing your point of aim too far.

Bart, I'm not bad mouthing anything. It would of been nice had you explain that what you posted was 2nd time. You seem to forget things like this.


I've used the following rule of thumb for several years to track the
accurate life of barrels shoot everything from PPC cases to very large
magnum cases in 30 caliber. It's proved very accurate, at least within
10% of what folks get. My data is bases on what competitive shooters get
for accurate barrel life. But hunters, plinkers, and other rifle shooters
will get the same results; the barrel doesn't know the shooting conditions
it's being used in. Whether or not the shooter-rifle-sights-ammo system
can tell when accuracy starts to get worse by a quarter or third MOA is
subject material for someone elses keyboard time.

 

[Bart B]

TOM H, I've no longer kept perfect track of post counts on my formula. After a dozen or more times it didn't matter.

Do you spend a lot of time keeping track of every post I make everywhere?

 

[TOM H]

TOM H, I've no longer kept perfect track of post counts on my formula. After a dozen or more times it didn't matter.

Do you spend a lot of time keeping track of every post I make everywhere?

Bart you do have a track record on your post just like your comment on 3 shot groups and you might want to read this also

These custom precision long range hunting rifles are meticulously assembled by and built with the best component parts from some of our many trusted LRH Sponsors.They come with a 1/2 inch, 3 shot, 100 yard accuracy guarantee. But most of my customers achieve groups better than that as shown in the sample of target pictures to the right.

For pricing examples look at the individual cartridge pages (links on upper left of all pages).

Len Backus
Owner, Long Range Rifles, LLC
Owner/Publisher, LongRangeHunting.com
920-379-2020 or Send Email

 

[Mikecr]

Mikecr, are you willing to share your App, so others can look at how powder ect, changes life expectancy?

I would certainly send it to anyone who asks for it.
I can't post a spreadsheet(even a tiny one) here.

barrelnut, the linked article and spreadsheet posted was a very early version that site had snatched up in error. I've asked them to replace it, they said they would, but apparently haven't.
There was an issue with life adjustment related to moly, and with an extreme underbore(the 30br).
So years ago I fixed it, and dropped the moly specific adjustment, because few still use moly, and fewer still know how to do so without actually shortening barrel life. This reminds of another factor that cannot be included: CLEANING

The base formula did come from Bart I believe(thanks Bart). That was a helluva long time ago. Since then I watched and queried for every posting & reporting of barrel life at pretty much all forums for over 10yrs. Slowly but surely the formula was enhanced until passing all credible tests. I have not seen an outright failure in it's prediction since(and I've watched for quite a while).

It's not going to give you an answer you believe or want. But it will give you truths, relative if you wish. There is an extending adjustment field available for those who have had their barrels melonite treated. There is not enough information available yet about barrel life there. Some are hopeful it will double, or triple barrel life. All of MY future barrels(and actions) will be treated.

Anyway, email me for a copy so that I can simply reply with it attached.