Physics behind "Push" vs "Snap"

Mainly it's the projectile's velocity to weight ratio. Higher-velocity rounds will tend to snap more, whereas the .45 is a big, slow round, and gives more of a push. In long guns, the analogy would be that a shotgun is a push, whereas a rifle is a kick.

Recoil impulse is dependant on many factors, the most important ones being mass of the gun, mass of the projectile, and velocity of the projectile.


Those three figures can be used to figure the missing fourth: velocity of the gun coming back towards you. Simple laws of physics, every action has an equal and opposite reaction. Different bullet weight and velocity will result in different gun velocity (i.e. recoil).

Velocity. The recoil is spread out over the duration of the firing of the gun. Slower the round, "slower the recoil"

What an interesting question! Here's my read:

We humans are used to thinking in terms of our own human time frame, and not necessarily that of the physical world. So what we define as a "snap," in our terms, is really an eternity compared to, say, the speed of light. Same with an automotive engine spinning at 10,000 rpm; though it's hard for us to conceive of it in this way, the four-stroke cycle is really occurring as slowly as molasses.

So I opine that the "snap" vs. "push" is really a function of the speed at which the powder flame propagates, or changes from a powder to a gas, assuming all other things are relatively equal. I think reloaders call it deflagration or something similar.

Please feel free to shoot me down on this, as it is only my notion, and I don't mind being corrected.

This suggests another question as well: Since there's always a muzzle rise upon ignition that tends to push the muzzle off target, is it logical to assume that the sooner the bullet leaves the influence of the moving barrel the better? In other words, all other factors being equal, is a faster-burning powder inherently more accurate?
On second thought, assuming the mass of the bullet remains constant, a greater force is required to increase its acceleration. Does a faster burning powder create a greater force?
Dang, that's more thinkin' and speculatin' than I'm accustomed to doing this early in the morning!

I'm going to hypothesize that the rate of change of momentum imparted to the shooter is the main factor for felt push/snap. Faster = snap, slower = push.

EDIT: Clarifying that the above is all related to, and can be defined with, force, mass, acceleration, etc.

Acceleration is velocity change over time -- ie, the derivative of velocity.
Force = Mass * Acceleration
Momentum = Mass * Velocity

Faster burning powder creates greater force to the extent that in generates higher acceleration of the bullet. What else might affect acceleration? Amount of powder, volume change upon combustion, caliber, barrel length, how much gas escapes via other routes than the barrel tip...

Does push/snap begin only after the bullet exits the barrel or before? If before, is POA/POI affected? If not, are we discussing perceived push/snap as opposed to a true difference?

It's a function of the curve of how the total amount of force is applied over time.

Assuming for the sake of argument the same total force, we can visualize how our 25 hypothetical units of force are distributed over time in a graph, which due to the limits of its character nature is arranged so that force increases to the right, and time increases going downwards.



"Snap":

----------force----------->
|*
|*
T***
I****************
M***
E*
|
V

"Push":
------Force-------->
|*
T*
I**
M***
E****
|*****
|******
|***
V

^ That's a good visual representation for what's going on. The longer it takes the bullet to leave the barrel (slower acceleration), the longer a force will be applied, and the "pushier" it will feel.

Not sure how great of an effect this would have but with the 40 being a higher pressure round could the forces of the compressed gasses leaving the muzzle after the bullet has left be the main factor. The 40 would decompress much faster than a 45 due to the greater pressures generated. Just a guess. So the big question is who has the equipment to start doing some tests?

I guess I am showing my age. I always thought it was called recoil.........chris3

My thinking is along the lines of grizz.
Pressure
.40 S&W: 33,000psi
.45 ACP: 21,000psi

Well, it wouldn't be velocity alone. A .45 can be loaded to .40 velocities with 165 grain or 185 grain slugs, but it still doesn't "snap".

Well, it wouldn't be velocity alone. A .45 can be loaded to .40 velocities with 165 grain or 185 grain slugs, but it still doesn't "snap".

Click to expand...

I submit that given a similar platform of the same weight (say, Glock vs Glock), a .45 loaded to .40 caliber specs in terms of bullet weight and muzzle velocity would have perceptibly identical recoil.

I am gonna go for the KISS answer:
People need different words to describe slower or faster recoil. Push=slower, snap=faster.

I submit that given a similar platform of the same weight (say, Glock vs Glock), a .45 loaded to .40 caliber specs in terms of bullet weight and muzzle velocity would have perceptibly identical recoil.

Click to expand...

Could be. Anybody got a matching set of .40 and .45 pistols?

I submit that given a similar platform of the same weight (say, Glock vs Glock), a .45 loaded to .40 caliber specs in terms of bullet weight and muzzle velocity would have perceptibly identical recoil.

Click to expand...

I agree (though actual recoil would be imperceptibly greater due to the lower pressure .45ACP requiring a bit more powder). In short, weight and the use of a heavier projectile (thus lower velocity) are the primary differences.

The rate of change in acceleration is called 'jerk.'

It occasionally comes into play, but is often so variable that it cannot be easily managed analytically.

Higher jerk indicates more of an impact than a push.

Given the same weapon and bullet mass, the higher the muzzle velocity will be snappier.

.44 special vs .44 magnum for example, same weight bullets and all, the .44 magnum will feel snappier TO ME.

I'm going to hypothesize that the rate of change of momentum imparted to the shooter is the main factor for felt push/snap.

Click to expand...

I'd agree with this and venture to say that slide velocity is probably a huge factor here, as it's the part that actually imparts the kinetic energy into our hand.

I would venture a guess that it's a shooter's imagination, probably due to the sound... one goes boom and the other goes bang. =o)