Double Barreled PUMP Shotgun

[insanebikerboy]

No, IBB, they system DOES NOT EXPERIENCE 2000fps.. It experiences double the mass thrown at 1000fps in a gun weighing twice as much. Its felt recoil would be ~ 2x the standard gun. NOT 4x.

Then what does the system experience if the velocity in one barrel is 1000 fps and the other is 1002 fps? It's not 1001.

 

[MasterBates]

To go with your assumption.. Lets take a 20g vs a 10g shotgun.

They both push pellets at ~1000fps.. Does the 10g somehow make it "more faster" because it is throwing about 2x the weight? NO.

 

[MasterBates]

The average velocity of all pellets would be 1001fps..

But you are throwing ~2 oz of shot vice the ~1oz you would have thrown with a single 12 ga slug/load.

 

[insanebikerboy]

To go with your assumption.. Lets take a 20g vs a 10g shotgun.

They both push pellets at ~1000fps.. Does the 10g somehow make it "more faster" because it is throwing about 2x the weight? NO.

If the weight of the everything coming out of the barrel is the same, the recoil is the same. The weights aren't the same so the recoil of the 10g is greater.

 

[MasterBates]

Yes.. And all the 2 12g barrels do is effectively make this a 6g gun.

They do nothing to increase the velocity of the ejecta.

 

[PropAddict]

What happens in your equations if you have the shot traveling at 1000 fps in barrel #1 and at 1002 fps in barrel #2? Which velocity do you use? And no, you can't average them, because you would then have to average everything in your equations.

Well, the most accurate way would be to insert the actual velocities into the equation.

e.g.:

• V1=1000 fps
• V2=1002 fps

Rearrange your gun velocity equation to reflect that the projectiles are going different velocities:

Vgun =(Mejecta1*V1+Mejecta2*V2) / Mgun

(For transparency, I removed your 7000 which is a conversion factor for American units and I collapsed the three ejecta masses{shot, wadding, powder} into one Mejecta term for each gun barrel.)

Basically, there are two sensible options left:

1) We grab two shotguns and recording scale and meet at Gateway Rifle and Pistol club to settle this Mythbusters style. I'll even buy the shells.

Or

2) You post saying something to the effect of, "Wow, I really !@#$%ed with you guys. I can't believe you let me string you along with bad physics arguments for 3 pages. And Prop even did a whole crap ton of calculations. You got punk'd!"

 

[C420sailor]

Master Bates and PropAddict are correct.

When finding momentum you can simply average the two velocities and sum the masses. When finding energy, you're better off finding the energy of each projectile individually and then adding them (because of the v^2).

But I failed out of mechanical engineering and went business, so what the hell do I know?

 

[mmx1]

Then what does the system experience if the velocity in one barrel is 1000 fps and the other is 1002 fps? It's not 1001.

What system? The system is stationary.

The gun (and you, if the butt is in your shoulder) experiences an impulse, not velocity, as a result of conservation of momentum. Impulse is additive. Velocity is not.

If only Flash could come onto this thread and give us an absolute answer and tell us who is "pissing in the wind", all of this could be settled. Where is that guy when we really need him?

Why bother, you already settled it in post 7. Everything else is just waiting for the lightbulb to go off (on?).

 

[C420sailor]

Deleted - looked it up

 

[insanebikerboy]

Ok, so after getting home I realize my argument is invalid for the doubling of the muzzle velocity. My apologies to all, after reading my notes my memory apparently isn't as good as I thought, I was confusing muzzle velocity with recoil velocity. Prop and MB, you guys are right about the muzzle velocity with a gross conceptual error on my part.

However, what velocity I should have been talking about was the recoil velocity, which will double as the barrels of the shotgun are fired at exactly the same time.

Here's why. The charge is doubled, which doubles the recoiling velocity of the gun as well as the recoil impulse of the gun, which results in a total increase in free recoil by a factor of four.

The equations notwithstanding I posted earlier, I'm going to use a calculator off of Handloads.com, because quite honestly I'm not going to fat finger the numbers and don't feel like scanning in handwritten notes. I'm also going to simulate using a double-barrel .308 instead of a shotgun, because these numbers I'm using below are actual numbers I've personally tested and recorded with handloads and a chronograph at the range, not just something made up for the sake of argument.


Load 1
168.2 gr Sierra HPBT
2631 fps bullet velocity
43.5 gr IMR 4064
10 lb M-1 Garand

Recoil Impulse - 2.74 lb-sec
Velocity of Recoiling M-1 - 8.81 fps
Free Recoil - 12.05 ft-lbs

Load 2 (everything is doubled)
336.4 gr Sierra HPBT
2631 fps bullet velocity
87 gr IMR 4064
10 lb M-1 Garand

Recoil Impulse - 5.47 lb-sec
Velocity of Recoiling M-1 - 17.62 fps
Free Recoil - 48.18 ft-lbs


48.18 / 12.05 = 3.99834!!!

So, while I'll readily admit I was retarded about which velocity was being doubled, the fact still remains that the total recoil of a gun that has both barrels shot at the exact same time is increased by a factor of FOUR and not two

 

[MasterBates]

IBB, you are neglecting that the weight of the double barreled shotgun is close to double of the standard single barrel.

So you'd need to plug a 20lb garand into your equations.

 

[MasterBates]

Put it this way.. If you bolted 2 M1s onto an instrumented sled and fired them both at the same time, you'd see the recoil force of 2 M1s. Not 4.

Now if you managed to make the 2 barrel 308 garand weigh the same as a stock single barrel, then your argument may start making sense.

 

[insanebikerboy]

IBB, you are neglecting that the weight of the double barreled shotgun is close to double of the standard single barrel.

So you'd need to plug a 20lb garand into your equations.

Put it this way.. If you bolted 2 M1s onto an instrumented sled and fired them both at the same time, you'd see the recoil force of 2 M1s. Not 4.

Now if you managed to make the 2 barrel 308 garand weigh the same as a stock single barrel, then your argument may start making sense.

All that doubling the weight of the gun is going to do is decrease the total amount of recoil felt, in your example what it would do is cut the recoil in half. It's a one to one relationship of gun weight to recoil.

Let's change the gun then, make it an actual double barrel shotgun with a single trigger that controls the sear for both hammers. This is actual data for black powder loads in a 12 gauge shotgun.

Load One
Bullet Weight in Gr: 820.3125
Velocity in fps: 1210
Powder charge in Gr: 110
Weight of firearm: 8lb

Recoil Impulse in Lbs sec: 6.36
Velocity of recoiling firearm (fps): 25.58
Free recoil energy in ft/lbs: 81.30


Load Two
Bullet Weight in Gr: 1640.625
Velocity in fps: 1210
Powder charge in Gr: 220
Weight of firearm: 8lb

Recoil Impulse in Lbs sec: 12.71
Velocity of recoiling firearm (fps): 51.16
Free recoil energy in ft/lbs: 325.18


The weight of the gun has nothing to do with the ratio of recoil if the shotgun is doubled.

 

[PropAddict]

Put it this way.. If you bolted 2 M1s onto an instrumented sled and fired them both at the same time, you'd see the recoil force of 2 M1s. Not 4.

MB beat me to it.

Your math is still off for not accounting for the extra weight of the second gun bolted on there.



Oh shit. We MIGHT have just created another Airplane/Treadmill semantics problem.

IBB, was your original assertion that if he takes that *double shotgun* and just fires one barrel of it, then takes that same double shotgun and fires both barrels at once that he has just quadrupled his recoil?

Because *that* case is actually true. (any of the equations with 6.6 kg for the gun weight plugged in all through will show you that. No fancy-schmancy internet calculator req'd.

This is because the added weight of the gun dampens the recoil of the one shot case and lowers it to 1/2 what the recoil would be of a single shotgun firing a single shell.

I was reading your original 4x post (and all subsequent, until the one right above this) as saying that firing the double shotgun will have 4x the recoil of firing a single shotgun, which remains patently untrue.

 

[insanebikerboy]

IBB, was your original assertion that if he takes that *double shotgun* and just fires one barrel of it, then takes that same double shotgun and fires both barrels at once that he has just quadrupled his recoil?

Because *that* case is actually true.

Which is what I have been saying all along. Shooting both barrels of a double barrel shotgun produces four times the amount of recoil.

That's what the equations I posted prove, and that's what the calculator I posted also proved.