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April 24, 2006

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Barrel Life, Part II

Bullets don’t wear out barrels, the flame from burning gunpowder melts them, so heat has everything to do with whether your barrel lives or dies tragically at an early age. The other factors are the size of the powder charge and the diameter of the bore.

Prairie dog shooters burn barrels faster than almost anyone else because they shoot quickly and they shoot a lot. When you get a tube smoking hot and keep it that way, its rifling is going to erode. Big-game hunters hardly ever burn out barrels unless they use their guns for other things. I have a .300 Weatherby that I’ve been hunting with since 1965, and the bore is good for another 41 years, simply because I don’t shoot it fast, or much. And the .300 Weatherby is often cited as one of the worst barrel-scorchers.

Powder charge weight versus bore size can be explained this way: For any given bore diameter, there is a maximum amount of powder that can be efficiently burned. In .30-caliber, I’d guess it’s something like 60 grains, so if you take a .300 Weatherby magnum and stuff in 84 grains, you have what is known as overbore capacity—a comparatively small gain in muzzle velocity produced by a huge increase in the powder charge. And the monster flame this creates reduces bore life to 1,500 or less from the 5,000 you normally get from a standard .30 cartridge.

But why worry?

Melvin Forbes, president of New Ultra Light Arms, was shooting prairie dogs a few years ago and had his barrel glowing an attractive cherry red when a friend asked him if he wasn’t worried about burning it out.

“Even as we speak,” said Melvin, “people are making barrels whether we want them to or not, and it takes me five minutes back at the shop to screw one in. But I don’t get to go prairie dog shooting that often.”

And then he went back to shooting.

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Comments

Cory

Amen to the last paragraph! If you wear out a gun - good for you! You are one of the few to do it. Enjoy the shooting, buy a different one later and hang the last one on the wall.

Mark

I remember shooting prairie dogs [really, they were gophers] in Montana. I’d take a centerfire rifle and a .22 [rifle and a handgun]. I’d go through 200-rounds of centerfire ammo and then most a brick of 22’s in an afternoon.

That was rifle sport shooting!!!!!! I cleaned my rifles for the first and only time for copper fouling on this sport.

I wish I wore out a rifle barrel by hunting.

BTY—How could Melvin hit anything with a rifle barrel that hot? My experience has been if my barrel was too hot, my bullets would walk all around in circle what I was attempting to hit. Discovered this many years ago trying to sight in.

Later.

Dave Petzal

To Mark: I was speaking figuratively. The only barrels I've actually seen glow are machine gun barrels. He just had his very, very hot.

Eric Olds at Gunsite

Dave,
Recently had a hunting rifle client ask me a question I couldn't definitively answer, viz: When I practice, especially in hot weather, how do I know when I'm about to get my barrel hot enough to do 'permanent' damage? All I could tell him is that when you see it start to change color, you've permanently altered (as in annealed)the steel. True or not? And is there a way to tell, short of that point, when it's time to stop shooting for a while?

Best, Eric

Bob

"For any given bore diameter, there is a maximum amount of powder that can be efficiently burned."

That doesn't sound right to me. Bore length, not diameter, must be the significant limit - a long bore gives the powder plenty of time to burn while a short bore lets the powder be wasted by flashing & burning in the air.

Think of the vastly different amounts of powder in the similar bore diameters of .22LR and .223.

Mickey Coleman

Eric, I'm not Dave, of course, but I don't think it's possible to shoot a bolt actioned rifle fast enough to change the color of the barrel. With a full auto? Very likely but you are correct when you say it is damaged if the color changes. You can ruin a HSS tool bit by grinding until it gets too hot and turns blue.

Dave Petzal

Eric:
I take a much more conservative view. Unless you're shooting a bull barrel, merely getting it hot enough that you can't keep your hand on it is going to shift your point of impact. Getting it hotter than that and continuing to shoot for protracted periods will shorter barrel life considerably, which can be considered a form of damage.
I'd go with Mickey. If it's an SS barrel and it changes color to the degree that you can see it, you've probably wrecked it.
By the way, I've seen Mickey Coleman turn blue and it's pretty scary. I favor something in fuschia.

Dave Petzal

To Bob:

If you had a 30-inch .300 Weatherby barrel you would probably burn all the powder before it hit the open air, but you would still get shorter barrel life than a .30/06 because you'd still be igniting a larger, hotter flame at the rear of the bore.
Also, who is going to take a 30-inch barrel hunting? Not I.

dan

Hey Dave, I just read an article on the web that you wrote about Savage 99's. You said to pass up a 99 chambered in .284? What are you stupid! Don't you realize the value it will hold? By the way in todays world you can get any ammo in any caliber shipped to you in three days. Better get with the times and understand the values of the 99.

Mark

Dave,
Just saw you wrote 1500 rounds For a 300 Win.mag.Ihave a browning A-bolt Thats probally 12 to 15 years old.I can account for at least 1200 or more rounds through this barrel after I started handloading.Prior to handloading I would say it's got at least 2 to 300 rounds of factory ammo through it.Problem is I can't get this gun to shoot anything anymore.The most accurate load in this gun was Hornady heavy mag 180 SP factory ammo.I've never been able to reproduce This type of accuracy at this velocity,wich is typical of the newer blended powder loads.3100 FPS through a chrony with a 26" barrel.I've tried every thing to get this gun to shoot but groups are twice the size they were 300 rounds ago,even with the factory ammo of the same lot.Do you think this barrel is shot? I've naver had it bore scoped and am considering having it rebarreled.Do you recommend anyone with experience working on A-bolts.For the record this gun shot .75 200 yrd. and .50 groups at 100 yrds.Lately,I've been lucky to get anything under 2.5" at 100 yrds.What should I do besides sell the rifle off?

Flip

Mark: You didn't mention anything about cleaning it - and I mean REALLY cleaning it - but before I'd spend the money to have it rebarreled, I'd try a "down to bare steel" cleaning. I've purchased several rifles from owners who were convinced the barrels were "shot out" and it's amazing how well they shot after they were squeaky clean. Took a few rounds to get em to settle down after cleaning, but they all shot well enough to more than justify the purchase price. Just my 2cents worth. Good luck.
Flip

Dr. Ralph

Flip, I was going to point him in that direction too. A serious scrubbing with Hoppe's No. 9 and copper brush will work wonders. Drive that thing in there like you mean it and always from the breach just stroke it. If that fails take your scope and mounts off and re-install... if it still won't shoot sell it to me cheap because I'll put a new barrel on a gun that shoots .75" at 200 yards.

Ed J

Mark
get some copper solvent and do what flip said. We did it to a 264 win that was suposedly shot out and got another 500 rds out of it. Then it was sot out and you could see the throat erosion.

Dr Ralph
Are you noting it in your 257 Wby. they're noted for being hard on barrels?

Dr. Ralph

I've shot about three boxes sighting in and playing when I first got it, shot five times at deer bringing four home (one had to be shot twice) and maybe forty or fifty rounds at the range just to keep it happy. Less than 150 rounds so it's probably not even broken in. I've carried my Rem '06 all this year just because I feel better with it in my hands. There's no doubt a .3" bullet kills better than a .25" bullet if it has enough velocity. I'm not a big fan of the hydrostatic shock theory and my 30-06 has never missed in my hands and every deer is less than 50 yards away deader than world peace...

the greater the hydrostatic shock the more internal damage theres going to be. Shoot a pumkin with a 30-30, then shoot one with a 30-06, you will see what hydrostatic shock is about.

you could even produce more hydrostatic shock with a smaller caliber than a large one, if the velocity of the smaller bore is great enough, and the bullet weight difference isnt too great.

here's an example of hydrostatic shock, I shot a buck with my .257 wea. mag., I completly missed the heart, but the extreme internal pressure caused by the bullet speed, blew it in half.(hydrostatic shock) And no, it wasn't because of a broken rib, it missed the ribs on entry.




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