Double Barreled PUMP Shotgun

[C420sailor]

I agree that the mass can be doubled if and only if the two joined weapons are fired at the same time---otherwise you would have LESS felt recoil (one round fired from a weapon that is now twice the weight).

And obviously there is a window within which the two would both have to fire, simply because the acceleration of the projectile and burning of the gases is not instantaneous.

What I don't agree on is the doubling of the velocity. 1000fps is 1000fps, regardless of how many projectiles there are---it is the mass that changes. Agree to disagree, I guess.

 

[Cron]

Don't mean to "feed the nerds", but here's a video of it in action. Maybe that can somehow aid this collective geektasy.

http://s180.photobucket.com/albums/x91/Captain_Kennedy/?action=view&current=PB210045.flv

 

[Bevo16]

That first shot where he hit both barrels nearly put him on his ass.

 

[a2b2c3]

I don't know about gun equations but F=ma. 'A' is the same with one gun or two, same end velocity. If you double the mass (for two projectiles) then you require double the force for the same 'a.'

So simple version, 2x force required. Now someone go find the complex equation that you can understand and that says otherwise. Until you do I'm gonna stick with this.

 

[xj220]

I'd be tempted to use that equation, but I've seen enough times where it's much more involved than that because of some X factor.

 

[PropAddict]

Damn it. Recoil increases by a factor of 2, not 4.

The only way to get 4x is to a) due the math wrong with numbers or b) make mistakes when manipulating the equations w/o numbers. Both InsaneBikerBoy's equations and mine from page one show, clearly, that it's 2x the recoil.

Here, I worked it out for you Statics-style in the attachments.


The only way to make it more clear would be to get a load cell, a couple of guns, and head to the range. I'm game for that anytime, especially with the next week off for the 4th. Thank you, VP-30!

 

[Bevo16]

who wants some:

funny thread fellas.

 

[insanebikerboy]

Nice Bevo. I'm seeing the conveyor belt/airplane thread developing. I actually just submitted this to Mythbusters!

Damn it. Recoil increases by a factor of 2, not 4.

Yes, if you use the velocity of only one barrel in the equations, the total increases by two. But, you have to sum the velocities for the equation to be correct. You look like you worked the equations properly, but you left out the doubled, summed, total velocity. To use only the velocity of one barrel discounts the other.


Let's think of it another way. Use the scenario that barrel #1 shoots at 1000 fps and barrel #2 shoots at 1001 fps. Assume both shots leave the barrel under the .003 seconds required (for the average length shotgun barrel) to make the recoil considered one impulse.

What is used as the velocity for the equation? If it's averaged, then you have to average everything that comes out of the barrels; wad, shot, powder, gas, etc. But, the reason that doesn't work is because the individual shot for each barrel is traveling at the 1 fps different speed. It's also possible that the powder charge is slightly different, the wadding weighs slightly different, etc, etc. So, if you average the values of everything then you've just taken the recoil of one barrel completely out of consideration.

The impulse of recoil is the big part here, because if the shots are far enough apart then the shots are considered separate and the total recoil is the sum of the two barrels. The shooter would feel this as two distinct impulses. However, if the shots leave the barrel within the same time frame it produces a single impulse of recoil, which is what would cause the total recoil to increase by a factor of four, because the velocities have to be summed for the single impulse.

The other thing to consider is that it's possible to have charges that aren't exactly the same produce velocities that are the same, due to other external factors such as heat, barrel condition, etc.

That's why the velocity has to double, because if it doesn't you're removing the factors contributed by both barrels.

 

[PropAddict]

No.

I agree we're talking about impulse (F * deltaT), which is equal to momentum change (M*deltaV).

The shot from gun #1 is M1 grams travelling V1 m/s, giving an impulse of M1V1-M1*0.

The shot from gun #2 is M2 grams travelling V2 m/s, imparting an impulse of M2V2-M2*0.

They both started from rest, so it's all gained momentum and we can drop out the zero terms in the summation.

Total Impulse=M1V1 + M2V2

That works for all cases, even if there is a slight split in the muzzle velocity generated.

We assumed the same rounds would have the same shot and powder masses and the same muzzle velocities, which is to say M1=M2 and V1=V2

Ergo, Impulse= M1V1 + M1V1 = (2M1)V1

This is exactly why we just double the masses in your gun velocity equation, but we don't also double the velocity. It's the distributive property, man.:icon_smil

Using a physical world analogue, reductio ad absurdem:

What you're trying to say is that in order in increase the muzzle velocity of our projectiles, all we have to do is duct tape a bunch of barrels side by side. When we fire this big pipe organ gun, all the bullets will have velocities multiplied by the number of projectiles going off at once, which is simply not true. The bullets will travel at the same speed they were going to go before. There will just be many more of them than if the guns were fired 1 by 1.

A flying example (because a jet engine throwing hot air out the back is fundamentally the same phenomena as a gun firing a bullet and smashing your shoulder with the stock):

When you fly along with symmetric power set on two engines and you shut one down, how much more power do you need to set on the operating engine? My FTI says I need to approximately double the power on the good engine to maintain altitude and airpseed, not quadruple it. Go ahead try it. I'll wait.

The engines, like the shotguns, are independent of each other. They could care less whether or not they have an identical twin operating in tandem. So, you sum the effects of each one. There's no synergy or funny power law relationship working here.

 

[Bevo16]

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?

 

[MasterBates]

IBB, your assumption that V is now 2000 fps is FLAWED AS ALL HELL..

What's moving at 2000fps? NOTHING

It's just moving twice the mass at the same speed. Nothing done to this gun doubles muzzle velocity.

<---- Engineer of shit that actually works, with a couple patents in my name.

 

[Picaroon]

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?

It's Flash. He has the opportunity to rile people up by not typing a reply and by God, he's going to use it!

 

[scoolbubba]

Haha I haven't checked this thread in a while.

All I can say is, with this Tiered technical major scholarship bullshit, we can look forward to more of the same as every new SNA wears coke bottle glasses and rocks a pocket protector in his flight suit. Nerds, all of you. Your spank socks probably have F=MA and E=MC^2 embroidered on them, don't they?

 

[insanebikerboy]

Stuff about momentum and engines

Prop, in your equations, the way you solved them, you are proving that the recoil doubles if you double the amount of shot, etc, in a single barrel. That's easily provable just like what you did. However, you're not dealing with a single barrel, you're dealing with two separate barrels that are acting on one single system, which is why you have to sum the velocities.

Answer this question, and it's not rhetorical. 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.

IBB, your assumption that V is now 2000 fps is FLAWED AS ALL HELL..

What's moving at 2000fps? NOTHING

MB, I never said anything is moving at 2000 fps. If you actually go back and read the posts you'll see that I said the individual barrels still shoot their respective shots at 1000 fps. The total velocity that the entire system experiences is 2000 fps. The reason for that is because you have two distinct, separate barrels. If you only had one barrel but double the weight of the shot, then the system would only experience a total of 1000 fps. The individual pellets still travel at 1000 fps in the individual barrels.

I'll ask you the same question as I just asked PA. What happens if you have a difference of 2 fps between the two barrels? If ignition occurs at the same time, the shots will be in the barrels at the same time. Which velocity do you use?


You have a patent or two? Big whoop, that doesn't make you the end all be all in mathematics and physics. Keep that shit in discussions at the bar on Saturday nights.

 

[MasterBates]

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.