Firecracking vs Barrel Steel

[Ggmac]

The way you clean your test barrels and if shot dry will also determine life .
The military did a lot of testing , and as previously stated , barrel steel AND the NUMBER OF HEAT /cool CYCLES . The heat and cool of surface steel will tend to crack from the barrel steel next to it that doesn't expand at the same rate as the hotter surface of the bore .
Sorry , no coffee yet !

 

[rardoin]

I understand the "way overbore" of short barrel life. But with the same cartridges and the same "everything", why do some barrels get about 30-40 percent less life?

I've experienced the same with a 6.5 Creemoor. Running 140gr Hybrids, H4350 at same velocity...one barrel had eroded at 800rds well past the distance two other barrels had at 1700+ rds. These were three different manufacturers chambered with the same reamer by the same gunsmith. I think the steel composition had a role to play here also as, like Ben, the variables of the load were the same.

Robin

 

[ScottVA]

I have operated large steam turbines for over 30 years and every turbine manufacturer will tell you that the faster you heat/cool that turbine metal, the less rotor cyclic life it will have and the sooner a crack will propagate. Meaning, if I take a rotor that is 100 degrees and heat it to full temperature of 900+ in 4 hours vs 24 hours, the rotor done in 4 hours has more stress placed in it and therefore fewer heat/cool cycles. I would think a barrel is the same. Also, is it not fairly certain that Norma brass is softer and therefore primer pockets loosen at a quicker rate? My vote goes to the quality of the steel coupled with rate of fire, heat/cool cycles as large contributors.

 

[6fatrat]

I agree that the more overbore the cartridge is the shorter the barrel life, also the rate of fire as in a match rifle shooting slow fire only compared to a XTC rifle shooting lots of rapid fire strings will also increase erosion.
The hardness or type of steel will also have an affect on erosion.
When I started shooting XTC in 1981 some shooters in the Bay city Michigan rifle league were shooting bolt actions in 30-06 will machine gun barrels that walked out the back door at the GM plants in Saginaw during WW 2.
These barrels showed very little wear after documented round counts in excess of 10,000!
Steve Bair

 

[Lefty Trigger]

There probably is something to it with the "quality" of the steel being a factor. This same thing applies to other things in our everyday life, like our cars. Autos built back in the 40's and 50's seem to have way better steel in their body. The metal resists rusting better and the metal welds better during repairs also resists bending and cracking better. Our new cars are rusted out in 5 years, the metal is nearly impossible to weld now without hassles (they are gluing some now,... seriously this is a thing) and they dent and ding if you look at them funny.
Old guns can sit in the safe or gun cabinet for years without being touched and look great doing it, modern guns rust if you breath near them. I believe the OP is on to something but it's beyond our control and most likely beyond the control of most barrel makers, they are at the mercy of their supplier and where the steel is coming from.

 

[PhilKeil]

First thanks for the great thread.
In Lefty trigger]s reply above, would it not all come down to predetermined obsolescence ? In the comment discussing barrels by 6fatrat, that went out the back door lasting large round counts to now barrels lasting very low counts would it not be possible to create a very high quality barrel but calculate it would only last a certain period or round count then you would have to replace it? For the better machinists than me would it not be more cost effect and easier on tooling to cut or button a softer steel than a harder steel alloy?

 

[Alex Wheeler]

There can be very large differences in barrel life do to steel. The bore scope will show large differences in cracking even in the same cartridge and barrel make. It seems like about 2 years ago many of us went through a batch that died really fast. The manufacturer was contacted and samples sent in. On the up side, the ones that go faster also seem to shoot a little better....

 

[ShootDots]

First thanks for the great thread.
In Lefty trigger]s reply above, would it not all come down to predetermined obsolescence ? In the comment discussing barrels by 6fatrat, that went out the back door lasting large round counts to now barrels lasting very low counts would it not be possible to create a very high quality barrel but calculate it would only last a certain period or round count then you would have to replace it? For the better machinists than me would it not be more cost effect and easier on tooling to cut or button a softer steel than a harder steel alloy?

I was speaking last night with my "old" gunsmith from Houston, where I came to Arizona from. I posed the same question to him that I am asking on this thread. His answer was that in the last "year or so" he has noticed (a certain barrel maker) that he can saw thru a barrel much quicker and machine it where he notices a "softer" steel cut. He inquired, informally, to some of his colleagues in 'smithing, if they noticed that same thing. They all did. His opinion is that they are STILL the most accurate barrels made and if we have to endure a lower round count, so be it. But his observations do smack of "planned obsolescence" in my opinion..

 

[dskogman]

It’s more of a cost/benefit thing I would guess. There are some extremely tough high temp SS alloys that ”may”make great barrels but would cost much more and require carbide tooling. A small custom barrel maker has to buy what’s available instead of ordering tons of a custom alloy.

 

[Kurz]

Still the question remains as to WHY that barrel's life was so short, when others were considerably longer under nearly identical circumstances.

My vote goes to the quality of the steel coupled with rate of fire, heat/cool cycles as large contributors.

I believe the OP is on to something but it's beyond our control and most likely beyond the control of most barrel makers, they are at the mercy of their supplier and where the steel is coming from.

There is no one reason for barrel life variances. All of the explanations above will fit into the entire picture of why these variances occur.

We bought 20 - 20ft sticks of barrel steel from the failed Bren Ten company. It was far less expensive than the 416 R from Crucible...

Normal process of drill, ream and cut rifle for many of the large caliber, high energy cartridges we worked with daily. We made one, a 416 Rigby, for an author who was invited to go to Africa on a hunt so he could write about the experience. While working up his loads for several bullets he noticed a slight degradation of group size but he continued shooting tests. The groups got worse. He called and we suggested sending the rifle back to us so we could examine it as a whole.

After two days of testing we discovered that the steel itself was about 10 points softer than the steel we used currently then. So we got samples from other barrel makers only to find that his barrel was disturbingly softer. We cut more samples from the original batch of steel which confirmed the soft state of the steel.

The first 6 - 8 inches in front of the chamber was toast, really poor shape. The rest of the barrel was suffering but o.k. We made a new barrel (new steel 416R Crucible) in double quick time, fitted it and got it back in time for him to work up loads for the trip. The barrel performed admirably in Africa.

Long to short; softer barrel steel, changes in the steel formula or the way the steel is stored and handled can have disastrous effects on rifle barrels. This is can also be compromised by high pressure, high energy cartridges. Like accuracy, there are a dozen or more potential problems which contribute to answering this question. It's not just a matter of one or the other.

 

[Texas10]

I would have to agree that it's all about the steel, and it's heat treatment. And that is where the Lothar Walther's barrels may be better, at least the ones made from their patented steel formula. But in the end, it's all about making a profit.

I spent the first decade of my aviation experience building hot section parts for military jet engines. First from 402 and 412 stainless which produced a very short service life, then Hastelloy which had 10X the life span in service. So I've seen how differences in steel and heat treatment can affect service life of parts subjected to rapid heating and cooling.

It seems logical that extreme over bore cartridges would destroy a barrel quicker, when you have more heat being applied for a longer period in the first few inches of the barrel. An extremely high and rapid temperature change is very hard on steel.

I just ran a new endoscope camera down the barrel of my 1898 Krag and was amazed at how pristine the lands and grooves were. Almost no firecracking, leade and lands in perfect condition, very few rust pits. This is in a barrel built over 120 years ago under a what was probably a "cost plus" government contract. I don't know if it's possible to find the steel specification used, but that might be an interesting line of study.

Given the narrow market we represent, as opposed to production rifles, I would have to agree that we just have to be prepared to shell out the coin for whatever we can get. We are the waste market for powder, and almost certainly the same for barrel steel.

 

[rogn]

Its my WASG that barrel steel/alloys are like baking a cake. You get the same cake every batch, but some are just better than others. There can be so many variables in baking a cake from the quality of individual ingredients to the vagaries in a heat cycle, ad nauseum. Being carefull and conscientious we get a good product but not always exactly the same.
Made what could be a mistake and bought a snake camera. As they say social media,OMG!!!!
The last barrel I had chambered was a known quality cut barrel which never shot exceptionally, and copper fouled like a plating machine. Not wanting to be a whiner I shot the thing and scrubbed and soaked. Best I could do was a couple of 1.5 moa at 600. Well I stuck the camera in there last nite(just got it) and have been crying all night. about 400 rounds +/-. This with a whopping 35.4 gr in a 6mm. 44 grains of water, so in a similar class as the 6.5 x 47L. about 800+ in the bore ratio scale. My 6.5x284 did better than that and still looks better! Fire cracking for about 6", some lands look like the edge of a cut slice of bread. One of the grooves has a ragged trough for abt 4-5 inches. Still a hint of copper after cleaning with Bore Tech and JB. It just has the appearance to me of a cake that wasnt stirred the right way or amount or used Missouri wheat instead of Kansas wheat and the alloy is let say 'deviant". I dont think the steel people or the barrel maker have complete control or culpability in this.
I guess Ill send it back to the barrel folk and see if the can make sense of it. Sense would be the best thing.

 

[LA50SHOOTER]

Better Steel will most certainly take longer to acquire than cheaper / less quality.

I know of one barrel maker who made / still makes 50 bmg caliber barrels. One barrel by a gentleman had a fully documented including bore scope photos over the +3000 round life of the barrel on a 50 bmg chambered barrel & he exclusively shot the 750 gr. Hornady A-max projectile & Hodgdon H-50BMG powder.
- It shot very well in competition (1000 yard FCSA) until the approx. 3500 round point where it gave up. - The Throat / Leade area was very deteriorated but the barrel still shot & grouped accurately. - I believe that the quality of steel (416R Stainless)had much to do with this.

The Quality & Cost of the steel is in the "hands" of our barrel makers.

- Ron -

 

[Dud]

Getting a custom lot of steel from a foundry requires an order of many tons. Not all barrel making operations have enough cash to tie up like that.

 

[Webster]

The way you clean your test barrels and if shot dry will also determine life .
The military did a lot of testing , and as previously stated , barrel steel AND the NUMBER OF HEAT /cool CYCLES . The heat and cool of surface steel will tend to crack from the barrel steel next to it that doesn't expand at the same rate as the hotter surface of the bore .
Sorry , no coffee yet !

All rifle barrels should be similar in hardness. The have to be machined with lathe and milling machine tool bits. The wear is not caused by friction. It's not related to the hardness of the metal. It’s called hot gas erosion. The wear is related to the melting temp of the metal which is about the same for carbon and SS barrels. The wear is caused by the temp of the gas, pressure and velocity of the gas.

https://www.nap.edu/read/18418/chapter/1
click next at the bottom of each page.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a328657.pdf

 

[Bill K]

I believe it comes down mostly too how fast and how hot you get the barrel, especially at the point of lead/chamber area. If you keep shooting when it is hot, it is going to erode faster than if you shoot a cooler barrel. Hot friction is your enemy and will take out a barrel faster than anything else.

 

[riflewoman]

The two documents referenced by Webster indicate that not much progress has been made in the forty odd years since I looked at erosion of gun tubes. So little in fact that there doesn’t appear to be any practical solution on the horizon.

Some barrel makers will have better luck that others but it might be more happenstance than by design.

 

[Straightshooter1]

All rifle barrels should be similar in hardness. The have to be machined with lathe and milling machine tool bits. The wear is not caused by friction. It's not related to the hardness of the metal. It’s called hot gas erosion. The wear is related to the melting temp of the metal which is about the same for carbon and SS barrels. The wear is caused by the temp of the gas, pressure and velocity of the gas.

https://www.nap.edu/read/18418/chapter/1
click next at the bottom of each page.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a328657.pdf

Some interesting informing. Thanks for the links.

One interesting thing that caught my eye on Pg. 16 on the nap.edu was that this:

"One important aspect that has not received enough attention is the formation of heat checks on the bore interface and roughening of the surface. Decoppering agents are claimed to increase the rate of growth of these thermal cracks and to increase the rate of wear. The life of a 3 inch trial gun was doubled by eliminating the decoppering additive from the ammunition."

Along this line, this is something I've recently been thinking about. When I look at the firecracking in my gun and see where copper has filled in, it seemed to me a good idea not to remove that copper as it fills in the cracks, which seems to me would reduce the friction that the firecracking would produce, thereby reducing wear of the lands.

In the past, I've been pretty aggressive when cleaning my barrels to remove everything from the steel surfaces. But lately, I've been leaving some of the copper fowling, and it seems to help. I've noticed in my Kreiger SS barrel that I've had for almost a year now, the lands is holding up pretty well (though that in part, I'm sure, is due to not so many hot loads as I've used before). Have got just over 2000 rounds down my .308 tube and the lands has only moved .007. Will have to see how the next 2000 down that tube does.

 

[Ggmac]

All rifle barrels should be similar in hardness. The have to be machined with lathe and milling machine tool bits. The wear is not caused by friction. It's not related to the hardness of the metal. It’s called hot gas erosion. The wear is related to the melting temp of the metal which is about the same for carbon and SS barrels. The wear is caused by the temp of the gas, pressure and velocity of the gas.

https://www.nap.edu/read/18418/chapter/1
click next at the bottom of each page.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a328657.pdf

Page 10 , 1 paragraph, page 16 paragraph 3 , I m only to 16 but have read this many times before, obviously my memory is mixing some other studies with the later tests of the military , after all this was 1975 . Seems like just yesterday . Now if I could only remember where the other studies were .
Page 35 (typed #)paragraph 4
Page 38 , typed # first full sentence .
Time to walk dogs , it seems I remembered just some of this data or it was what the instructor thought was most important.
What I forgot or never understood (1975) was anti copper additives and the SHORT barrel life . I wonder what the new copper removing powders are doing to our barrels , if anything?

 

[ebb]

Riflewoman fire cracking large magnum barrels was certainly not academic when my group could shoot out at the sugar mill any time we wanted and I was younger.