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How much muzzle energy (recoil) is OK in your opinion?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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How much muzzle energy (recoil) is OK in your opinion?

Unread postAuthor: High-PSI » Sun Jan 08, 2012 7:06 pm

Hey Guys,

In general, I just enjoy building and firing my cannons, no matter how much power I have. However, for fun, I have been moving to higher and higher pressures just to see how far I can take it, and I am encountering the added recoil associated with it.

Anyway, how much power have you guys run and what seems to be acceptable as far as recoil goes? GGDT says my big cannon is capable of over 3,000 ft lbs of muzzle energy. The cannon weighs over 30 pounds and that helps absorb the recoil, but at 1,500 ft lbs muzzle energy I have been firing at up until now, the recoil feels pretty solid.

What are your thoughts?

Matt
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Unread postAuthor: SpudBlaster15 » Sun Jan 08, 2012 7:44 pm

Well, you can start by calculating the free recoil energy and comparing it to listed values for common firearm cartridges. This should give you a pretty good idea of what to expect. For most launcher setups, the recoil energy can be calculated with reasonable accuracy using this formula:

E<sub>recoil</sub> = 1/2m<sub>launcher</sub>[(m<sub>projectile</sub> + m<sub>gas</sub>)v<sub>muzzle</sub>/m<sub>launcher</sub>]<sup>2</sup>

For a real world example, my 30lb shoulder fired hybrid cannon is capable of about 3000-4000ft-lbs depending on the preignition pressure and projectile mass. With the correct firing stance, the recoil is manageable with any round ~160g and under. Not comfortable by any means, but manageable.
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Unread postAuthor: Fnord » Sun Jan 08, 2012 8:45 pm

I believe acceptable recoil force is normally less than 100 ft-lbs, though some large shotguns, typically four and two-gauge, may have been as high as 500 ft-lbs. They were usually quite dangerous to the shooter though.
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Unread postAuthor: High-PSI » Sun Jan 08, 2012 9:13 pm

My cannon is a shoulder fired and kicks pretty hard at 1,500 ft lbs of muzzle energy. However, it is not painful. A shotgun smacks the shoulder with a quick "Rap!", my cannon hits the shoulder with much force, but with more of a hard push than a rap (I hope I am am making sense). Anyway, as I up the pressure, I guess the best thing is to up it a bit at a time to see how the recoil feels.

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Unread postAuthor: MrCrowley » Sun Jan 08, 2012 9:59 pm

I have a similar cannon, with similar performance, to SpudBlaster15's and like him I don't have too much trouble with recoil. I wouldn't hesitate in firing the cannon with projectiles around the 160g mark, I haven't done so yet as I've got the similar muzzle energies through higher mixes with lighter projectiles rather than heavier projectiles at slightly lower mixes.

The cross bar on my cannon makes it reasonably comfortable to be hip-fired, without it I used to prepare for injuries after each shot.
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Unread postAuthor: jackssmirkingrevenge » Mon Jan 09, 2012 1:39 am

The thing with recoil is that while it can be calculated, how you perceive it is highly subjective, not only related to muzzle energy. As you said, spudguns tend to give an impulse over a longer time than a firearm so there is a difference in perceived recoil. Heavier launchers also tend to mitigate felt recoil because they can better absorb the force.

There are steps you can take in order to make it acceptable, we've already discussed muzzle brakes but you can also have the chamber and barrel mounted on a rail on which it is free to recoil, suitably dampened by bungee chords, a gas strut from automotive suspension, large spring etc.
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Unread postAuthor: Zeus » Mon Jan 09, 2012 3:12 am

Honestly, it's all in stance. My light 12GA kicks like a mule if you don't get a solid grip on the (fore stock, bit at the front), but if you've got it nicely, then it's pleasant to shoot.

And you say a shotgun is snappy with recoil? I take it you've never fired any of the .30 magnum family.

The best way to handle recoil is to do what I do, become a recoil whore.
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Unread postAuthor: Daltonultra » Mon Jan 09, 2012 5:38 am

Having fired a .700 Nitro Express side-by-side rifle, I'm not too impressed by the recoil from most potato guns. (The rifle knocked me three steps backward, and left a bruise from my nipple to halfway down my bicep...) That said, when I tried shoulder-firing a can of ravioli from my 3"x10' sprinkler valve cannon, I hit the ground wallet-first, you might say. There is definitely a limit to how large an object you want to fire with one of these things without having some sort of stand.

BTW, GGDT says muzzle energy for mine is somewhere around 2400+ft/lbs.
For comparisons sake, the .700NE puts out ~8,900ft/lbs.
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