Why do shorter barreled guns have more recoil?

[doc2rn]

I always thought the gasses expanded behind the projectile forcing it out the front thus putting a backwards inertia on the web of the hand causing the barrel to rise and thus recoil is percieved. I also thought that was why we see some cutting from those gasses on the inside of shot out S&W revo's. Or maybe I am wrong again. My .02

 

[Funderb]

I don't think bruises are psychological.
Light does not make me imagine extra force on my shoulder.
Simply put - the m44 mosin has more recoil than the m91/30

 

[GLOOB]

I always thought that the mass and velocity of the bullet had a lot more to do with recoil than the gases rocketing the gun backwards.. like on the order of 99% to 1%.

The smaller, faster bullets cause more recoil. But they are also produce more kinetic energy. A 230 grain 860 fps hardball produces, what, a few hundred foot pounds (I'm guessing, here)? A 180 grain 1200 fps produced on the order of 460 ft lbs, or so (again, a guess).

A rocket has to have a specific shape to the nozzle to be effective, at all. And a muzzle is definitely NOT a good likeness of a rocket nozzle.

But the compensator guys can't be all wrong.

Now, if someone would just build a 1911 barrel with a rocket nozzle on the end, we could all find out for sure.

 

[jeepmor]

You have six axes of motion. 3 linear dimensions, X, Y and Z, and three rotational components around the axes of X, Y and Z.

Effectively, and more simply mathematically, KE1=KE2

KE = kinetic energy = 1/2mv^2

KE1=gun
KE2=bullet

Fast bullet, slow gun because guns weigh more. Less gun mass, less recoil, that simple.

When you get into elaborate physics calcs, we talk about all six of these axes simultaneously, which is all the energy components that make up the recoil. We have to assume the bullet left the barrel. Not entirely true, but we're talking milliseconds, so not an issue. All that energy is imparted back to the user of said firearm.

This recoil is largely determined by the form factor of the firearm.

How far is the axis of the bullet above the grip?
What's the form factor. Moment of interia in x,y,z axes.
What's the muzzle twist of the barrel?
What's the bullet mass?

It all comes into play. This is why small 9mm mouse can whomp you more than and weighty range magnum.

 

[Funderb]

I think as a side note that the exit gasses do contribute to recoil when directed in frot of the rifle. Otherwise there wouldn't be much of a market for muzzle brakes. So, 99.99% of felt recoil is after the round leaves the barrel. There isn't enough time to feel it before the round leaves. You can't process it that fast, nor has the energy reached the butt to shoulder contact enough to take effect.

 

[1911Tuner]

So, 99.99% of felt recoil is after the round leaves the barrel

Not in this universe, I'm afraid.

At no point are the forces greater than at peak pressure...which occurs very quickly after the powder ignites and the action/reaction event begins.

Pressure drops off quickly after the peak, and how quick depends on several factors...the main one being powder burn rate...but pressure in the system at the point of bullet exit is a small percentage of the peak.

In certain rifle calibers, with sharp shoulders and light bullet to powder charge ratios...the impulse after the bullet exit can nearly equal that generated by the bullet...but such isn't the norm.

Hypothetical...

Double-end, smooth-bore cannon. Bore diameter is precisely the same, with zero variation from one muzzle to the other.

Two cannon balls. Each one exactly the same in weight/mass...diameter...and each one perfectly round.

Powder charge located precisely in the center of the cannon barrel, with both balls seated precisely equidistant from its respective muzzle.

What will happen when you fire the charge?

 

[Funderb]

The problem with that is that a rifle is not an exact tuned double ended cannon of perfection.
just look at how long it takes the bullet to leave the barrel, and how long it takes a person to notice the brunt of the recoil.

 

[1911Tuner]

just look at how long it takes the bullet to leave the barrel, and how long it takes a person to notice the brunt of the recoil.

All duly noted and factored in...but the plain, simple truth is that the reaction is instantaneous. You can't push on an object without being pushed, and whatever measure of force that you impose is immediately returned to you in like measure. There is no delay, and there is no such thing as force in one direction...and then force in another direction at some later point. Can't happen. Force forward equals force backward. The movement of recoil that you experience after bullet exit is momentum. Whatever impulse is generated by the escaping gasses behind the bullet are equal to the mass of the gasses...which is roughly equivalent to the unburned powder's...and it doesn't amount to much, because momentum is Mass X Velocity.

F'rinstance:

.45 ACP. Normally about 5 grains of powder in the case. Gasses escape at roughly the speed of sound...let's say a thousand fps for simplicity's sake. The recoil impulse will be about 1/8th that of a standard velocity .22 rimfire.

Newton 3:

For every action, there must be an equal and opposite reaction. Equal means equal...both in magnitude and in the time frames involved. Whatever force is necessary to accelerate the bullet is immediately placed on the breechblock.