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question about recoil

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question about recoil

Unread postAuthor: ramses » Sat Dec 20, 2008 10:29 pm

I am curious about where the force of recoil is actually applied. I am curious because I will be building a piston hybrid and if I could get away with some sch80 fittings in some places, I would love to spend less.

Which of the 3 places in the craptastic paint diagram do you think the recoil force will be applied to? If 1 or 3, do you think a sch80 PVC bell reducer would be able to take the recoil from a max of 13,000 foot-pounds. The barrel will be 3".

Sorry if this is the wrong forum, I thought it should go here because it is more about gun physics than anything. if you disagree, move it.
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Unread postAuthor: jonnyboy » Sat Dec 20, 2008 10:36 pm

Based on very limited knowledge of firearms shouldn't it be the point where the gas turns 180 degrees to the barrel?
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Unread postAuthor: IA_Armourer » Sat Dec 20, 2008 11:01 pm

long answer: recoil is the result of the law of physics which goes something like this. "every action has an equal and opposite reaction" so where ever there is force been applied when firing is where recoil will come from.

short answer: EVERYWHERE
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Unread postAuthor: ramses » Sat Dec 20, 2008 11:06 pm

yeah, I knew about the 3rd law. the question is where this recoil is transmitted. to. If there is recoil at the whole back, that is fine, it will be metal.

do you think a 3" sch80 pvc bell reducer can take 13,000 ft-lbs worth of recoil?

Or should I use cell core to take away some of the sectional density of the pvc shrapnel that will hit me as a result of trying?
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Unread postAuthor: VH_man » Sun Dec 21, 2008 12:02 am

What you CAN do is attach some method of spreading that force over a long time, say

reduce impulse, Which is the force divided by the time its spread over, If i remember correctly.

Aka, Get some springs, Padding, ECT.

Also, Figure out where force is applied. and 15,000 ft/lbs of recoil force..... ? I feel you didnt do that correctly. I beleive even a high power hunting rifle is only around 24 ft/lbs..........
Make sure you count in the inertia of the firearm itself.

Also, If i havent answered your qustion, the force will be applied at the point of contact with the object. So technically, there is a multitude of equal and opposing forces....

The force of recoil will be acting rearwards on any peice of the launcher also launching the projectile, AKA, part 3 does NOT count as where the recoil force originates.

Id say with a hybrid, DO NOT GO SKIMPY!!!!!
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Unread postAuthor: jackssmirkingrevenge » Sun Dec 21, 2008 2:10 am

IA_Armourer wrote:where ever there is force been applied when firing is where recoil will come from.

short answer: EVERYWHERE


Short answer is THE BARREL actually.

The recoil is a reaction to the linear motion of the projectile and escape of propellant gasses, this happens in the barrel and therefore it is where recoil forces are applied. The recoil is then transmitted to the rest of the launcher through wherever the barrel is attached.

Some firearms like the Barrett M82 use this effect to mitigate felt recoil by allowing the barrel to recoil separately within the frame of the gun, an action which also works the reloading mechanism.
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Unread postAuthor: ALIHISGREAT » Sun Dec 21, 2008 4:57 am

i really would't use PVC on a hybrid unless you reinforce it anyway... so why not just cut it out and use metal all the way?
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Unread postAuthor: psycix » Sun Dec 21, 2008 7:26 am

The recoil is not a force that is applied somewhere, it is the counterpart of a force that is NOT applied somewhere.
The force acted out on the projectile does not act out on the gun, leaving all pressure on the opposite side act out on the gun without a counterforce.

In the case of your diagram, the recoil would be acted out on the areas marked by 3.


The force acting on those areas will be exactly the same as all other parts of the gun (pressure). Only difference is that this part has no counterforce to neutralize it.
If you want to know whether the sch80 bell reducer can take it just think: can it handle the pressure it will be subjected to if it was used in a pressure chamber?
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Unread postAuthor: ramses » Sun Dec 21, 2008 10:08 am

I am not concerned with the pressure, just the shock/ moving force. I didn't count the launcher's inertia. and ALIHISGREAT, 3" metal pipe is rather expensive. sch80 pvc is cheaper, and sch40 has been used with no problems.

Psycix, that was a good answer.
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Unread postAuthor: SpudBlaster15 » Sun Dec 21, 2008 6:23 pm

VH_man wrote:reduce impulse, Which is the force divided by the time its spread over, If i remember correctly.

Aka, Get some springs, Padding, ECT.


No, impulse is change in momentum, which is the applied force multiplied by the duration of the force. Impulse = Force * Time, and you can't change it. A launcher's backward momentum is constant given a constant projectile velocity and gas/projectile mass. Thus, the change in momentum (Impulse) required to return it to zero is always constant.

Springs and padding do not reduce impulse. They reduce the recoil force by changing the kinetic recoil energy into elastic potential energy.
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Unread postAuthor: VH_man » Sun Dec 21, 2008 7:14 pm

SpudBlaster15 wrote:
VH_man wrote:reduce impulse, Which is the force divided by the time its spread over, If i remember correctly.

Aka, Get some springs, Padding, ECT.


No, impulse is change in momentum, which is the applied force multiplied by the duration of the force. Impulse = Force * Time, and you can't change it. A launcher's backward momentum is constant given a constant projectile velocity and gas/projectile mass. Thus, the change in momentum (Impulse) required to return it to zero is always constant.

Springs and padding do not reduce impulse. They reduce the recoil force by changing the kinetic recoil energy into elastic potential energy.


Meh, I need to stop reaching back into things my parents told me when I was 6 and finish freaking HS physics........
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