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Barrel Torque

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Barrel Torque

Unread postAuthor: Trauts » Wed Apr 05, 2017 3:57 pm

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I am making a bolt action mechanism and I am concerned about forces on the barrel.

In most bolt actions I've seen people using a sleeve to cover a hole in the barrel. This is functional but it always leaves a large amount of dead space between the hole and valve opening point. It also typically limits one to only using spherical ammo (because the hole gets too big for much else). This is why I want to make a floating barrel mechanism. I can insert any kind of ammo into the rear of the barrel and then push it back far enough to eliminate almost all dead space.

The one issue with this however, is that I foresee a lot of torquing on the barrel. When my ideal barrel is thin-walled copper tube I can see this being problematic. In the diagram I quickly made, the purple arrows indicate the loading I'd expect to see when firing. The bolt would latch into the body to lock in place and take most of the load. But because of the offset, the barrel would have to resist some twisting load as well and this is where I see an issue arising.

I'm wondering if anyone knows of any good ways to lock a bolt action floating barrel in place? Thanks!!!
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Re: Barrel Torque

Unread postAuthor: farcticox1 » Wed Apr 05, 2017 5:39 pm

Could you make a double sided locking bolt so there would be no twisting torque ?

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Re: Barrel Torque

Unread postAuthor: Trauts » Wed Apr 05, 2017 6:29 pm

The issue I see with that is the bolt not being used would be sticking upwards as you turn the opposite one down
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Re: Barrel Torque

Unread postAuthor: farcticox1 » Wed Apr 05, 2017 6:58 pm

that's a top view
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Re: Barrel Torque

Unread postAuthor: Trauts » Wed Apr 05, 2017 7:10 pm

On a typical bolt, the arm rotates down to about 30 degrees from straight down, so a bolt on the opposite side would be 30 degrees from straight up
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Re: Barrel Torque

Unread postAuthor: Anatine Duo » Wed Apr 05, 2017 7:18 pm

The opposite bolt "handle" can be concealed in a sleeve that has a channel cut out... it gets complicated to actually build though. I have several designs to deal with this but I wouldn't worry about it for a copper pipe build. I have wanted to try your design for a while. I call it the "reverse bolt action".
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Re: Barrel Torque

Unread postAuthor: WizardNoodle » Wed Apr 05, 2017 7:22 pm

Trauts wrote:The issue I see with that is the bolt not being used would be sticking upwards as you turn the opposite one down


Why don't you just cut the bolt that would be interfering with you down to be the same height as the sleeve?
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Re: Barrel Torque

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Re: Barrel Torque

Unread postAuthor: Trauts » Wed Apr 05, 2017 7:25 pm

As Mr. Due stated, that does get more complicated. If both handles aren't perfectly in contact, the loading is still uneven. I may give it a try with one and see if I don't encounter any issues
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Re: Barrel Torque

Unread postAuthor: D_Hall » Wed Apr 05, 2017 7:56 pm

Admittedly, I couldn't make heads or tails out of the original sketch, but.... Where is this torque coming from?
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Re: Barrel Torque

Unread postAuthor: Trauts » Wed Apr 05, 2017 8:13 pm

Force is applied (air pressure) to the barrel and it is only held from moving forward because of the bolt. This bolt would be held via the frame and this frame is offset. This causes a moment arm and strain on the barrel
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Re: Barrel Torque

Unread postAuthor: jackssmirkingrevenge » Thu Apr 06, 2017 6:04 am

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Better presented diagram.

To be honest the forces on the barrel are probably not as bad as you are expecting...

Let's say you have a 0.5" OD barrel with 0.02" walls, and you're firing at 500 psi.

The force on the barrel is - at worst - 15 lbs.
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Re: Barrel Torque

Unread postAuthor: Trauts » Thu Apr 06, 2017 7:27 am

True - I think I'm probably just being overly cautious. I'll be building soon and I'll hopefully have the results posted. Thanks very much people
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Re: Barrel Torque

Unread postAuthor: D_Hall » Thu Apr 06, 2017 10:42 am

Trauts wrote:Force is applied (air pressure) to the barrel and it is only held from moving forward because of the bolt. This bolt would be held via the frame and this frame is offset. This causes a moment arm and strain on the barrel


If I understand what has been said so far, your barrel is just a tube; the breech is a separate assembly, correct? If so, then the only longitudinal force the barrel experience comes from nothing more than friction. Your moment is negligable (unless your projectile is in there really F'ing tight).
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