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Why barrels will not last...

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/18/2013 at 08:05
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Did you ever ponder over these facts: (and please let the maths gurus check my facts)
 
Assumptions:
Bullet lenth= 1inch.
Bullet speed = 3000ft per second
Number of rounds fired = 3000
Powder charge = 50gr
Barrel life = 3000 rounds
 
Now the amazing stuff:
3000 bullets have a total length of 250 ft.
At 3000ft per second the 250 ft get pushed through the barrel in .08 of a second!!
A total of 21 pounds of powder is burnt in .08 of a second.
 
And we want barrels to last !!
 
The total life of a barrel is thus .08 of a second!!!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/18/2013 at 09:48
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WOW South of the equator. Winter, even so it, is a little early for cabin fever to be setting in.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/18/2013 at 10:31
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Neither the math nor the physics is correct, but it is a nice sentiment.

Technically, the bullet accelerates from standstill to 3000fps while it is in the barrel.  It does not traverse the whole barrel length at 3000fps.  Also, since the force on the bullet due to expanding gases is not constant, the acceleration is not constant either.  

If you assume that the acceleration is constant and a typical barrel is 24 inches (2 feet), and accept the rest of your assumptions, the bullet spends 1.33msec in side a barrel.

If the barrel life is 3000 rounds, it has been subjected to the trauma of a bullet travelling through it for approximately four seconds.

Now, with all that out of the way, the bullet itself does almost nothing to damage the barrel.  The damage comes from hot gases and powder residue, not from the bullet itself.

Oh, and yes, cabin fever sets in all over the world, Lile...  don't ask me how I know.

ILya
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/18/2013 at 12:03
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http://www.squidoo.com/cabin-fever-illness  
 Cabin Fever can be found anywhere  is related to isolation and confined spaces, Darker shorter daylight of winter leads to increased occurrences. The original implication was that some people have too much time on there hands. Leading to nit picking trivial matters. It is present everywhere, Your point was proven.  Whacko
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/18/2013 at 17:17
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" Hot gases, huh? "   






Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/19/2013 at 04:12
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/19/2013 at 09:25
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THAT is a horrible thought... 
 
You have a way of bending minds, 8's...  "oh, the humanity"...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/19/2013 at 10:23
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Barrel Steel and minds
expand and contract.
Chip away, chip away
until nothing is left.
Primal need applies the pressure
Menus change, but who's the cook?




Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/19/2013 at 12:17
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Wow... that was poignant, inspiring, and creepy all at the same time, Alan!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/19/2013 at 12:36
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The "angel" is Yolandi Visser. She's probably known to Wooter as she is a South African singer/entertainer in a group called Die Antwoord.
She's either brilliant or just a nasty little thing...




Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/19/2013 at 15:05
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Still a neat way of looking at barrel life. Four seconds of high temperature gas cutting life.

As for the chick I'm going towards the nasty little thing.

Try zooming in on her left eye in the second picture.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/19/2013 at 15:22
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Definitely road hard and put away wet. Bad helmet !!!

Whacko


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/19/2013 at 21:32
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If all this is true, then can someone explain how machinegun barrels can last many thousand of rounds? In WWI the water cooled machine guns on both sides would fire over 100,000 rounds in a day, and still be serviceable for the next day's fighting. In WWII air cooled barrels were heavier to absorb and disapate more heat, and had to be fired in shorter burst, but still lasted almost as long. Even quick change barrels lasted a long time, if changed at the appropriate time.
Granted, we're not talking about the same level of accuracy, but what falls into servicability for us.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/20/2013 at 15:08
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Originally posted by BeltFed BeltFed wrote:

If all this is true, then can someone explain how machinegun barrels can last many thousand of rounds? In WWI the water cooled machine guns on both sides would fire over 100,000 rounds in a day, and still be serviceable for the next day's fighting. In WWII air cooled barrels were heavier to absorb and disapate more heat, and had to be fired in shorter burst, but still lasted almost as long. Even quick change barrels lasted a long time, if changed at the appropriate time.
Granted, we're not talking about the same level of accuracy, but what falls into servicability for us.
 
I cannot explain how they last, exept that I can also relate to that. We fired machine gun and FN 308 barrels red hot and they were still good for a few thousand rounds. Or so we thought. We never did shoot 5 shot groups with a 20mm Browning. But we did spray them wildly in the right direction !!! Who cared about accuracy, as long as their was lead in the air...
 
On the other hand calibers loaded hot, or small bore to load ratios, definately do not last beyond 3000 rounds and still give a decent level of accuracy.
 
My last barrel threw flyers that would not hit a 12 inch target at 200 yds. The throat was toasted.
 
Most hunters do not fire enough rounds in a lifetime to test their rifles barrel life, so they do not give it a second thought.  Say 50 rounds a year for 30 years = 1500 rounds. On hunting loads and calibers this is nothing. But talk to the competition guys who go through a 1000 rounds + a year, then the 4 secs of flame torch stuff starts to count.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/20/2013 at 16:37
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Secret to long barrel life? Stay away from:

1. Overheating barrel by continuous firing
2. Overbore calibers that use large amounts of slow burning powder trying to exit down a small caliber hole

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/04/2013 at 13:50
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What if you use moly bullets and cote the barrel with moly?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/04/2013 at 14:15
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Originally posted by B W M B W M wrote:

What if you use moly bullets and cote the barrel with moly?


Like everything else gun related you get different opinions from the experts.

Here is an article by david tubb about moly bullets. 
http://riflemansjournal.blogspot.com/2009/09/moly-coating-david-tubb.html

THis is from Lilja rifle barrels

Quote

Q. What is your opinion of the use of moly coated bullets?

A. First, as described in our section on barrel break-in, we do not recommend the use of moly coated bullets for break-in. The break-in process requires the use of an uncoated jacket if it is to be successful.

Secondly, at the risk of offending those that promote the use of moly, we can't see much benefit to it for a couple of reasons. There are two basic claims made for the use of moly, reduced fouling and increased barrel life. We'll look at both of these.

We agree that bullet jacket fouling in a barrel can and will cause accuracy problems in a barrel. But for the most part, jacket fouling in a hand-lapped, match-grade barrel is minimal. For the small amount of copper fouling that does remain in most barrels, conventional cleaning methods can and will stay on top of the fouling. We recommend cleaning solutions like Shooter's Choice and/or GM Top engine cleaner mixed with Kroil oil and the limited use of Sweet's solvent. Our suggestions for cleaning can be found in the Cleaning and Break-in section.

We have examined barrels with our bore scope that have had an excessive amount of moly fouling layered with powder and jacket fouling. The only way we could remove this buildup was through relapping of the barrel. Perhaps part of this type of problem results from a mindset that says "Hey, I'm using moly now and I don't have to clean very often." So if you do elect to use moly coated bullets we recommend that you still clean as often as before.

So, the obvious question to us is, if regular cleaning is still required with moly and if a bullet/cartridge/barrel combination does not foul to any great degree without moly, what is the advantage to moly?

This leads us to the second part of our answer. Some of the promoters of moly claim an increase in barrel life. While this sounds good on the surface we must ask the question: what causes a barrel to shoot out? Barrels wear out, or no longer shoot up to their original performance levels, because of erosion to the throat area of the barrel. This erosion is caused by heat and pressure created by burning powder. As a throat lengthens, velocities fall off and accuracy can suffer too. Eventually more and more of the throat will be eroded and moved forward. Also the diameter of this eroded section will increase. We have seen take-off barrels that had fully 1/2 of the length of the rifling completely eroded.

The key to this type of erosion is that it is caused by hot powder gases under high pressures and not by friction between the bullet and the barrel. We have read a report from a military test that examined this type of barrel wear. It was found that over the course of tens of thousands of rounds the actual groove diameter of the barrel was only increased by a few ten thousandths of an inch. It is this type of wear that moly might prevent or slow down. But in this test the throat area grew progressively longer and larger in diameter from gas erosion, not friction between the bullet and barrel.

So from our point of view, moly coated bullets are not going to prevent the type of throat erosion we have described, that the type of wear caused by friction between the bullet and barrel is insignificant, and that the prevention of jacket fouling through the use of moly is marginal at best and that moly may add another type of fouling to the barrel.

There is one type of shooting that may benefit from the use of moly coated bullets, in our opinion. In an effort to find the "perfect" bullet, target shooters using the 50BMG cartridge have manufactured solid bullets that are lathe-turned from materials like brass, bronze, copper and even soft steel alloys. These bullets can cause a considerable amount of barrel wear caused by friction between the barrel and bullet. The bore and groove diameters of these barrels do increase in diameter as a direct result of this friction. And this wear is not caused by the hot powder gases that will erode a throat in more conventional barrels.

In this case it seems as though, in our testing, that coating bullets with moly will help reduce this type of barrel wear.

We realize that our opinion of moly does not go along with the wisdom and promotions of the day. But we're willing to listen to opposing views if you have one.

Post Script:  In the January, 1999 issue of PRECISION SHOOTING  Magazine there is an excellent article by Kevin Thomas of Sierra Bullets about his experiences with moly.  I would suggest that anyone considering using moly read that article first.  In summary, Kevin found almost the same results as we've outlined above.  In short he found that moly had no effect on extending barrel life in their controlled accuracy testing of bullets during production.  He did not see any improvement in accuracy and to the contrary even found some degradation in accuracy at times, and that moly could create its own fouling problems.  Mr. Thomas found that moly did reduce jacket fouling a little but that a regular cleaning schedule was still required.  Like us he wondered what if any benefit there was to using moly?

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/04/2013 at 14:30
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The real benefit to using moly is for those who sell it... profits...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/04/2013 at 23:16
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I think I may have one AR now that has about 16 seconds of use so far.  I might be a touch behind the curve with it.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/05/2013 at 17:04
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Originally posted by sakomato sakomato wrote:

Secret to long barrel life? Stay away from:

1. Overheating barrel by continuous firing
2. Overbore calibers that use large amounts of slow burning powder trying to exit down a small caliber hole

Hmmm, this is interesting. Most of the tac-precision crowd has gone to light recoiling, but way over-bore rifles such as the 243 Win. Most complain about barrel life, but many are saying that barrel life can be EXTENDED by using a slower burning powder. They explain by stating, a slower burning powder will burn all the way down the barrel, not just in the throat. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/06/2013 at 12:15
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Originally posted by BeltFed BeltFed wrote:

If all this is true, then can someone explain how machinegun barrels can last many thousand of rounds? In WWI the water cooled machine guns on both sides would fire over 100,000 rounds in a day, and still be serviceable for the next day's fighting. In WWII air cooled barrels were heavier to absorb and disapate more heat, and had to be fired in shorter burst, but still lasted almost as long. Even quick change barrels lasted a long time, if changed at the appropriate time.
Granted, we're not talking about the same level of accuracy, but what falls into servicability for us.
 
Servicability, meaning it still functions. Unless it warps or bows it keeps their heads down. I've also seen em glow red but as long as the straight edge laid flat on it, it stayed in service. Never saw one that was "accurate" anyhow. The water cooled was a good design. There may have actually been some notion of accuracy in those. Just a guess cause haven't had hands on one of those. Funny thing I experienced is the most "accurate" machine type gun I had hands on was the MK19. With all the bells and whistles you could consistently drop a three round push on a 3 meter area out to 1200 meters. That was some fun shootin!!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/07/2013 at 12:51
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Originally posted by billyburl2 billyburl2 wrote:

Originally posted by sakomato sakomato wrote:

Secret to long barrel life? Stay away from:

1. Overheating barrel by continuous firing
2. Overbore calibers that use large amounts of slow burning powder trying to exit down a small caliber hole

Hmmm, this is interesting. Most of the tac-precision crowd has gone to light recoiling, but way over-bore rifles such as the 243 Win. Most complain about barrel life, but many are saying that barrel life can be EXTENDED by using a slower burning powder. They explain by stating, a slower burning powder will burn all the way down the barrel, not just in the throat. 
Higher velocities are often reached by using greater volumes of slow powders. That means you're forcing more pounds of erosive gases (powder) down the bore.
Barrel erosion is initiated by expansion/contraction of the barrel steel due to the high pressures of firing a round. That flexing produces micro- cracks in the steel which are then chipped away by high pressure gases.
Any barrel- life strategy begins by minimizing both pressure and erosive- gas producing powder, while achieving the desired ballistic goal.
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