How thick does a barrel really have to be?


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Owen Sparks
September 8, 2008, 05:59 PM
I have noticed that many older shotguns that the barrels look almost paper thin in comparison to the muzzles of new models. Also, vintage revolvers had much slimmer barrels. Ever notice how thin the barrel of a 1911 is? Now we all know that with handguns a thick heavy barrel that puts more weight up front helps control recoil, and that thick stiff barrels on rifles vibrate less and are more accurate. But how thick do they really need to be in order to be safe? I chanced to handle a lightweight Taurus revolver over the week end and noticed that the barrel actually had a stainless steel liner. The forcing cone, that is the little stub of barrel that extends inside the frame about
1/8th of an inch with walls no thicker than a piece of copper water line. In fact, the cylinder walls on most revolvers like the S&W
.44 Magnum are surprisingly thin. You would think that if something were to fail under pressure, these parts would be like the weak link in a chain. This leads me to believe that with modern metallurgy that barrels could be made shockingly thin and still be perfectly safe, if not as accurate.

Just an observation, OS

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blackcash88
September 8, 2008, 06:22 PM
It's the CHAMBER that needs to contain the pressure and experiences the highest peak pressure during ignition and just prior to getting the bullet to start moving. The pressure in the barrel isn't nearly that high because the gases are expanding down the length of the barrel pushing the bullet out. The sidewall of the barrel isn't under that much stress.

jerkface11
September 8, 2008, 06:54 PM
My guess is that they're made thicker now to save machining time which means they're cheaper to make.

Thernlund
September 8, 2008, 06:59 PM
It's not the thickness necessarily. It's the geometry.

Loose example: Try to crush an egg long ways.


-T.

32winspl
September 8, 2008, 07:06 PM
Regarding the relative thickness of shotgun bbls (at least at the muzzle), I'm going to guess that it has something to do with the availability of screw-in chokes. However, that is just a guess on my part.

Zedo
September 8, 2008, 07:09 PM
You're getting into metallurgy and physics. --

You're just not going to find someone in these forums qualified in either field.

Varmint Al is a structural engineer, retired from Lawrence-Livermore National Laboratory . . . "the atom bomb people."

You can kick around his site. He has some articles about stress and working pressures.

www.varmintal.com

Look at some of his engineering and barrel harmonics pages, rifle action stress . . .

Zedo
September 8, 2008, 07:15 PM
Full-Auto forum glitch . . .

:banghead: :what: :banghead: :eek: :banghead: :fire: :banghead: :cuss: :banghead:

Josh Aston
September 8, 2008, 07:22 PM
Check out the KelTec P3AT (likely the Ruger LCP also). That thing has a shockingly thin barrel.

230RN
September 8, 2008, 07:45 PM
In the course of experiments on receivers (Springfield 03 --tat) some years ago, I used pressures up to 130000 pounds without any apparent ill effects on the barrels. The late Sir Charles Ross, whom I knew well, had told me about his experiments on the thickness of barrels, and I had read some remarks by Newton on the same subject, but I couldn't get sufficiently authentic facts to satisfy me, so I collected some first-hand information by turning a Springfield barrel to 1/8 inch wall thickness and firing it with regular and high pressure (proof -tat) cartridges. As the results were not visible, I turned the barrel down so that it was only 1/16 inch thick over the chamber.. I then put a 75000 pound shot through which blew a piece out of the side , as can be seen in the photograph. As the thickness of the regular barrel at this point is 5/16 inch thick, it is plainly evident that the strength should be sufficient." --Hatcher's Notebook, "The strength of military rifles," pp 201-202

My scanner isn't installed, so I can't scan the images.

The biggest reason burst barrels may occur, barring barrel obstructions, is with bad metal... seams of slag that somehow get incorporated.

Bear in mind that in firing, almost all the stresses on the barrel are tensional, and that it takes a lot less material to contain inside pressure than it does to "contain" a vacuum.

You can probably pressurize a beer can to 100 psi, but pump air out of it so that only 14.7 psi (at sea level) is pressing on it from the outside, and it will collapse.

The reason for this is that under pressure, the tensional forces in the walls of the vessel tend to equalize, but under outside pressure, that is, with the vessel evacuated, the walls are under compression, and any weak spot will tend to collapse further, resulting in a catastrophic failure of the vessel.

Put it this way: if you could grab aholt of the beer can, you'd never be able to pull it apart. Yet crushing one is relatively easy.

--Terry, "tat"

Cannonball888
September 8, 2008, 09:53 PM
Check out the KelTec P3AT (likely the Ruger LCP also). That thing has a shockingly thin barrel.
Scary thin. That's why I won't use Buffalo Bore .380 +P in my P3AT

545days
September 8, 2008, 10:36 PM
Of course those old revolvers were prone to bulged barrels too. It is the first defect I look for when checking out an old S&W.

makarovnik
September 9, 2008, 01:21 AM
Funny. I've noticed the opposite. The new barrels are much thinner than the old ones and lots of alloy receivers. Some of these new pump shotguns are so light they really beat you up when you pull the trigger.

JohnBT
September 9, 2008, 08:13 AM
"I'm going to guess that it has something to do with the availability of screw-in chokes. However, that is just a guess on my part."

But a very good one. It's not the chokes, it's the lazy way they do them. Another factor in the increase in barrel weight is the use of overbored barrels. Assuming they've kept the wall thickness the same when they make the larger diameter barrel, a large pipe (new improved large bore bbl.) has to weigh more than a small pipe (standard diameter for the gauge bbl.).

(Backboring is when you remove metal from a barrel bore to open it up - it makes the barrel lighter and the walls thinner.)

www.shotgunreport.com/TechTech/TechnicalTracts/ChokePort.html

"Most factory screw chokes added muzzle weight. This is because the
factories did it, shall we say, inexpensively. They simply bulged the
barrel at the muzzle, threaded it and popped in a big, fat, heavy choke.
In addition to saving production costs, this method was strong.
Unfortunately, it was also heavy because the weight of the screw chokes
was added to the original weight of the barrel. Recently Beretta,
Perazzi and some Rugers have gone to lighter chokes in non-bulged
barrels. A set of standard after market extended chokes for the popular
Citori weighs about two ounces- a tremendous amount of weight to add
right on the end of the barrel. To get around added muzzle weight many
of the best British shooters buy fixed choke guns (Mirokou 3800s and 38s
currently) and then get them screw choked. Aftermarket choke
installations only replace metal which has been removed and keep the
muzzle weight on those 32" barrels manageable. If you have a gun with
factory screw chokes, take them out and test the balance of your gun.
This is the way that your gun was originally designed to feel."

Eric F
September 9, 2008, 09:58 AM
Perhaps its a case of the kind of metal used v/s pressures. You might need more of a lighter weight alloy to holde the same pressure of a heavier alloy.


Speaking of thich barrels, I saw an octogon barrled flint lock made in the late 1700's it was a 32 cal but the barrel measured 1.75 inches outside to outside(has nothing to do with this thread but looked odd)

Vaarok
September 9, 2008, 10:17 AM
There's some very old discussion about this, and what I recall was that you can even get a bullet to pass down extremely thin barrels, so long as there's a gradual pressure spike and it's perfectly round.

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