Double Barreled PUMP Shotgun

[C420sailor]

Why are you doubling the velocity again? 1300fps is 1300fps, whether it is from one shotgun or ten. I agree that total projectile (for the weapon) mass, gas, powder, whatever doubles, but not velocity.

If it has 4x the recoil, then it must have 4x the muzzle energy too. That energy has to come from somewhere. And, as we all know, there is no free lunch.

 

[PropAddict]

Why are you doubling the velocity again? 1300fps is 1300fps, whether it is from one shotgun or ten. I agree that total projectile (for the weapon) mass, gas, powder, whatever doubles, but not velocity.

He means double Vg in his second equation, methinks. Which would seem logical if all you did in his first equation was double all the masses. The problem is you need to ALSO divide by double the gun mass (Wg) in that first equation.

 

[jfulginiti]

What the f@#$?! Why do threads about cool jets and guns keep turning into nerd math discussions?

 

[Hubble]

So, if you run those equations for a 3 inch, 12 gauge shell with a 1 3/4 shot charge, you'll get an approximate recoil of about 55 ft-lbs. If you double the velocity though, you'll see in the equation that results in a factor of 4, so the total recoil is actually about 220 ft-lbs.

Sorry man, another engineer kicking in here - I don't think your assumption here about doubling the velocity is accurate. You're doubling the discharged mass, yes, but not the velocity.

 

[insanebikerboy]

Why are you doubling the velocity again? 1300fps is 1300fps, whether it is from one shotgun or ten. I agree that total projectile (for the weapon) mass, gas, powder, whatever doubles, but not velocity.

I'm trying to find the equation. I had to push the I believe button at first too till I could prove it. The best example I can give is imagine the muzzle velocities as two voltages in series, they are summed.

If it has 4x the recoil, then it must have 4x the muzzle energy too. That energy has to come from somewhere. And, as we all know, there is no free lunch.

Not true, muzzle energy and recoil are not the same because the weight of the bullet is so much less than the weight of the gun. Couple of hundred grains vice 7-10 pounds (7000 grains equal 1 pound).If that were true, each time I fired my M-1 I'd be absorbing 3,000 pounds of energy through my shoulder. I'm not that tough....yet

Yes, it will help with how it feels on your shoulder, but that only changes perceived recoil, the total is still roughly the same.

I misspoke here. After reviewing my notes, recoil definitely decreases as the weight of the gun increase, if the cartridge being fired stays the same. The recoil for a 3 in 12 gauge in a 5 pound gun is about 34 ft-lbs, but in a 9 pound gun it's about 19 ft-lbs.

 

[Hubble]

What the f@#$?! Why do threads about cool jets and guns keep turning into nerd math discussions?

Because engineers design the toys pilots and gun people play with. Otherwise both groups would have a much higher fatality rate. <grin>

 

[C420sailor]

Not the same, but proportional. If 500ft*lb of muzzle energy out of a Rem 870 produces 20lb of recoil force, then 1000ft*lb of muzzle energy (from a hotter load, or firing two rounds simultaneously) should produce 40lb of recoil force. You can't have four times the original recoil if you only double the original muzzle energy without also cutting shotgun weight by half.

Think about it this way---you're shooting a Glock at the range. You decide that two is more fun, so you shoot them simultaneously, one in each hand. Does felt recoil of each pistol double? Of course not! Total felt recoil doubles, but each hand feels exactly the same. Now you tack weld (or in this case, epoxy!) them together and repeat---no difference.

 

[insanebikerboy]

Sorry man, another engineer kicking in here - I don't think your assumption here about doubling the velocity is accurate. You're doubling the discharged mass, yes, but not the velocity.

Both guns individually have the same velocity, for example 1000 fps. The total velocity in the firing of both barrels is 2000 fps. Counting only the velocity of one barrel would be removing the recoil felt from the other gun. You have to sum the velocities otherwise you're discounting the impact the second barrel would have. The equation isn't saying that the velocity of the individual pellets coming out of the separate barrels is 2000 fps, only that the total velocity required for recoil is 2000 fps.

Of course, the total time frame is about .003 seconds to shoot the barrels at the same time, otherwise there would be two distinct impulses and only double the recoil, since the shot of the first barrel has left the muzzle before the second shot is ignited.

 

[jfulginiti]

Because engineers design the toys pilots and gun people play with. Otherwise both groups would have a much higher fatality rate. <grin>

Okay good point.

 

[insanebikerboy]

Not the same, but proportional. If 500ft*lb of muzzle energy out of a Rem 870 produces 20lb of recoil force, then 1000ft*lb of muzzle energy (from a hotter load, or firing two rounds simultaneously) should produce 40lb of recoil force. You can't have four times the original recoil if you only double the original muzzle energy without also cutting shotgun weight by half.

Well, except that the equation for kinetic energy is KE = 1/2 mV^2. So, since a higher velocity would be required to produce the higher muzzle energy in your example, the recoil force would also be different. The squared term in the equation makes the results non-linear, which is what you were assuming.

 

[insanebikerboy]

Think about it this way---you're shooting a Glock at the range. You decide that two is more fun, so you shoot them simultaneously, one in each hand. Does felt recoil of each pistol double? Of course not! Total felt recoil doubles, but each hand feels exactly the same. Now you tack weld (or in this case, epoxy!) them together and repeat---no difference.

If you could fire both guns at literally the exact same instant then the recoil impulse has now become a singularity. As a result, they can easily be summed together since they are effectively acting at the same time. Hence, the total recoil in your example will again increase by a factor of 4 and not merely 2.

 

[Bevo16]

What the f@#$?! Why do threads about cool jets and guns keep turning into nerd math discussions?

Well, in college, some people thought this was "protection".

And others thought this was "protection".

The first group starts the gun threads. The second group starts talking equations.

 

[insanebikerboy]

Well, at least my mom thought I was cool.

 

[xj220]

Philosophers and historians talk about the world, engineers build it.

 

[insanebikerboy]

Philosophers and historians talk about the world, engineers build it.

And people who understand both go out and set records.