Physics behind "Push" vs "Snap"


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RTR_RTR
March 17, 2011, 04:28 AM
Hey guys,

Push (.45) vs snap (.40) recoil came up in a thread a while back, and I couldn't figure why this might be. Anyone have any solid knowledge or or want to just hypothesize for that matter? The three most logical things I can think of are barrel height relative to hand (higher, more snap), gun weight (higher, more push), and powder burn rate (higher, more snap). The gun-related factors would obviously be contingent on, well, the gun used, but there may be trends in design between the guns firing the respective caliburs (e.g. all metal 1911 .45, polymer frame glock .40).

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WardenWolf
March 17, 2011, 04:40 AM
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.

General Geoff
March 17, 2011, 04:41 AM
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).

Cryogaijin
March 17, 2011, 04:44 AM
Velocity. The recoil is spread out over the duration of the firing of the gun. Slower the round, "slower the recoil"

SleazyRider
March 17, 2011, 05:35 AM
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.

RTR_RTR
March 17, 2011, 05:55 AM
Sleazy, that's actually one of the things I'm leaning toward, if I wasn't clear in my op.

I'm not sure I buy the velocity argument. Velocity alone doesn't have any direct relationship that I can see in HOW a gun will kick - just to what degree, and that's only assuming increases in velocity over an equivalent time span (i.e. impulse).

My rationale behind the quicker burning powder is less time to react to the kick, thus having the brunt of the force taken in the wrists, which don't have enough reaction time to respond properly by locking up.

SleazyRider
March 17, 2011, 06:14 AM
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!

fletcher
March 17, 2011, 07:05 AM
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.

btg3
March 17, 2011, 07:16 AM
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?

geekWithA.45
March 17, 2011, 08:45 AM
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

fletcher
March 17, 2011, 09:02 AM
^ 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.

grizz13
March 17, 2011, 11:06 AM
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?

ball3006
March 17, 2011, 11:13 AM
I guess I am showing my age. I always thought it was called recoil.........chris3

DoubleTapDrew
March 17, 2011, 12:12 PM
My thinking is along the lines of grizz.
Pressure
.40 S&W: 33,000psi
.45 ACP: 21,000psi

Walkalong
March 17, 2011, 12:15 PM
^ 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.
Yep.

It is the velocity reached and the quickness with which it gets there that gives a push or a snap.

KodiakBeer
March 17, 2011, 12:20 PM
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".

General Geoff
March 17, 2011, 12:23 PM
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".

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.

LKB3rd
March 17, 2011, 12:31 PM
I am gonna go for the KISS answer:
People need different words to describe slower or faster recoil. Push=slower, snap=faster.

KodiakBeer
March 17, 2011, 12:39 PM
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.

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

Maverick223
March 17, 2011, 12:49 PM
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 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.

:)

brickeyee
March 17, 2011, 01:23 PM
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.

NMGonzo
March 17, 2011, 01:50 PM
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.

Nushif
March 17, 2011, 02:05 PM
I'm going to hypothesize that the rate of change of momentum imparted to the shooter is the main factor for felt push/snap.

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.

awgrizzly
March 18, 2011, 12:45 AM
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)

Walkalong
March 18, 2011, 08:52 AM
Nope.

Maverick223
March 18, 2011, 11:41 AM
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.I disagree; IMO the .45ACP is noticeably louder and is unquestionably less snappy with two similar pistols (but as is typical, built on different frames).

:)

Manco
March 18, 2011, 11:45 AM
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.

The thing about slide velocity (for autoloading pistols) is that it's dependent only on recoil (momentum) and the mass of the slide itself. This would seem to imply that two loads of two different calibers that happen to have the same recoil impulse (based on bullet momentum) would cause the slide to move at the same velocity, and that the recoil would therefore feel the same in similar weapons (of similar mass). The physical reality is a bit more complex since the slide is coupled to the frame through the recoil spring, but unless somebody can show how this or other factors that have not yet been covered here could result in a noticeable difference in the recoil force curve, there theoretically should not be an inherently qualitative difference between the "push" of .45 ACP and the "snap" of .40 S&W--they should feel pretty much the same.

By the way, while I have to say that I've felt such a difference when shooting these two calibers back-to-back, as is common these days the .45 ACP pistol was significantly heavier, so that doesn't count--the pistols have to be of similar weight for the comparison to be fair.

btg3
March 18, 2011, 11:48 AM
Just for further mental gymnastics, think about identical handguns pointed at each other with the barrel tips touching. Assume that we are able to fire a bullet from one gun cleanly into the barrel of the other gun.

Is recoil the same or different for the 2 guns?

Maverick223
March 18, 2011, 11:58 AM
Just for further mental gymnastics, think about identical handguns pointed at each other with the barrel tips touching. Assume that we are able to fire a bullet from one gun cleanly into the barrel of the other gun.

Is recoil the same or different for the 2 guns?Different. The second gun (the one "catching the bullet") doesn't have the additional recoil from the powder charge, nor is all of the energy transmitted (due to a small amount of loss).

:)

ball3006
March 18, 2011, 12:22 PM
You guys with all your theroy make my head hurt. chris3

Pilot
March 19, 2011, 08:04 AM
Can you feel a difference in snap vs push between slower burning powders and faster burning powders or is this negligible?

Ohio Gun Guy
March 19, 2011, 09:07 AM
F=M*A


Below is a good refresher....


http://www.physicsclassroom.com/class/newtlaws/u2l3a.cfm

Maverick223
March 19, 2011, 10:49 AM
Can you feel a difference in snap vs push between slower burning powders and faster burning powders or is this negligible?If the velocity and bullet weight is the same (which isn't typical) then the recoil should be as well (assuming the same amount of powder consumed); in other words, I don't believe the burn rate is important. The recoil due to powder mass is dwarfed by that of the projectile mass and therefore of little significance to begin with. I certainly can't tell a difference when a different powder is used to produce similar performance (though it is usually a similar powder weight to attain such performance). That said, I only handload for rifle cartridges, pistol may be a bit different.

:)

Deanimator
March 19, 2011, 10:52 AM
It's just a matter of time/pressure curve.

The more pressure over a shorter period of time, the sharper the recoil impulse.

Deanimator
March 19, 2011, 10:56 AM
If the velocity and bullet weight is the same (which isn't typical) then the recoil should be as well (assuming the same amount of powder consumed); in other words, I don't believe the burn rate is important. The recoil due to powder mass is dwarfed by that of the projectile mass and therefore of little significance to begin with. I certainly can't tell a difference when a different powder is used to produce similar performance (though it is usually a similar powder weight to attain such performance). That said, I only handload for rifle cartridges, pistol may be a bit different.
I'm betting you mostly stick to powders of roughly the same speed, like 4895, 4064, etc. 4895 and 4350 definitely feel different in a .30-06. 4350 is a MUCH slower powder, slow enough to bend the op rod of a Garand.

Maverick223
March 19, 2011, 11:28 AM
For the most part I do stick to powders with similar properties (especially in the higher recoil cartridges, like .375H&H and .45-70Govt., where you might be able to discern a smaller difference). I still doubt that there is a great deal of difference if you are able to achieve similar ballistics.

:)

MacTech
March 19, 2011, 11:52 AM
I'm wondering how much case volume has to do with this as well, I may just test a theory this weekend, I'll load up some .45 ACP cartridges with a maximum load of Unique or W231, and put that same powder volume in a .45 Colt case as well, try each round in my Ruger New Model Blackhawk .45 Convertible, that should minimize variables, the only difference between the two configs will be the insignificant weight difference between the .45 ACP and .45 Colt cylinders

My guess is that the Colt loads will have less felt recoil as there's more expansion room and that should keep the internal pressure low

same primers, powder and bullet (200 Gn LSWC), the only variable will be the size and volume of the cartridge case

Haxby
March 19, 2011, 12:16 PM
I don't own an autoloader, but I have shot a few over the years. You're talking about comparing perceived recoil. Can't you change the felt recoil by simply changing the recoil spring, and thus changing the amount of time over which the recoil force is exerted?

MacTech - with the same components in a 45 ACP and a 45 Colt, the Colt will presumably have a much lower velocity. Less pressure, less velocity, less recoil.

BeerSleeper
March 19, 2011, 12:31 PM
Just for further mental gymnastics, think about identical handguns pointed at each other with the barrel tips touching. Assume that we are able to fire a bullet from one gun cleanly into the barrel of the other gun.

Is recoil the same or different for the 2 guns?
It depends on how you quantify recoil. In terms of energy, nearly the same. The differences would be do to the firing pistol also "feeling" the recoil of the burned powder ejecta, and the more gradual acceleration of the bullet. The firing pistol is recoiling from the acceleration of the bullet over the length of the barrel (say 4"). The "catching" pistol will "feel" essentially no recoil until the bullet hits the end of the barrel, in which moment it will essentially instantaneously absorb the full energy of the bullet in a much shorter period of time than the firing pistol (again, nearly instantaneously). If one could feel the recoil of each pistol, I imagine one would compare the firing pistol as more of a "push" type feel, and the catching one as more of a "snap" type feel.

Maverick223
March 19, 2011, 01:21 PM
MacTech - with the same components in a 45 ACP and a 45 Colt, the Colt will presumably have a much lower velocity. Less pressure, less velocity, less recoil.I agree, add enough additional powder to keep the velocity the same and the .45LC should have more recoil.

:)

brickeyee
March 19, 2011, 01:32 PM
While the recoil impulse (total energy) may be the same, there is obviously a difference between the duration of the impulses.

We detect that as a push vs. a blow (as in sharp strike).

It shows up in odd places, and different ways.

Impact loading is a very different thing depending on the strength (area) of the impluse and how quickly it is delivered.

If you pushed gently on an object for 10 minutes you might barely damage it.

Deliver the same impulse using a hammer and you may have a different outcome.

awgrizzly
March 19, 2011, 01:49 PM
Among all the variables involved the greatest variable is perhaps perception, and what one expects to experience. You can load dissimilar cartridges with identical powder loads and the same weight bullets to eliminate as many variables as possible but still feel push vs snap based upon expectations. So to eliminate this the test would need to be a blind one, where the shooter doesn't know which caliber he is shooting. If there is still a definite difference, then I'd expect it to be a difference in volume on the cartridge producing different pressures, and/or the respective volumes of the barrels producing differing rates of gasses filling the void.

I still maintain that the sound of the discharge can greatly influence a person's perception of recoil. Take for instance that the flinch is a (p)reaction based solely upon expectation, and is as much a result of noise as it is of recoil.

Deanimator
March 19, 2011, 03:32 PM
For the most part I do stick to powders with similar properties (especially in the higher recoil cartridges, like .375H&H and .45-70Govt., where you might be able to discern a smaller difference). I still doubt that there is a great deal of difference if you are able to achieve similar ballistics.
You're still not allowing for the amount of time in which a given pressure is generated.

There's a big difference between Unique and Bullseye. The former is far more likely to give you a push than a smack.

Combustion velocity makes a BIG difference, both in explosives and propellants. It's the difference between blasting agent and PETN. People don't cut rails with blasting agent and they don't move earth with detonating cord.

Maverick223
March 19, 2011, 09:55 PM
You're still not allowing for the amount of time in which a given pressure is generated.I'm still not entirely convinced that there is a significant difference, but like I mentioned earlier I don't handload for pistol cartridges, yet (I plan to start loading 9mmPara. and/or .45ACP when I purchase a pistol caliber carbine), so I may be incorrect.

:)

Nuclear
March 20, 2011, 07:05 PM
I keep hearing people discount the mass and velocity (pressure) of the gasses coming out of the end of the gun. If you ever shoot a suppressed weapon with and without the suppressor on, using the same ammo, you will notice a significant reduction in recoil that is not a subjective expectation (suppressor work mainly by retarding the gases released from the muzzle). Even a +p 45ACP operates at a lower pressure than the 40S&W.

BeerSleeper
March 20, 2011, 09:32 PM
That is likely due more to the weight of the suppressor hanging off the end of the barrel. It adds mass to the gun. Also, that mass is added further out from the guns center of mass, thereby increasing moment of intertia, which reduces recoil induced muzzle flip.

in a typical 9mm loading, the bullet has a mass of 124 grains, while the powder charge is in the 6-7 grain range. In this case, the mass of the gasses account for 5% of the total projectile. Not substantial, but also not insignificant.

RTR_RTR
March 20, 2011, 11:30 PM
If I understand suppressors right, there's also going to be some muzzle brake effect with the gases, but yeah, still a small portion of the overall impulse.

Maverick223
March 21, 2011, 12:48 AM
That is likely due more to the weight of the suppressor hanging off the end of the barrel. It adds mass to the gun. Also, that mass is added further out from the guns center of mass, thereby increasing moment of intertia, which reduces recoil induced muzzle flip.No, a sound moderator often affords greater recoil reduction than a good brake up to .338LM (whereas larger cartridges have proven to work best with a brake). This is not due to added weight (because the reduction is far greater than that what can be attributed to the weight alone), but rather due to redirecting gases back to the shooter (much like a muzzle brake, though obviously in a slightly different manner resulting in sound reduction rather than an increase in perceived noise).

:)

SSN Vet
March 21, 2011, 10:11 AM
one word answer.... Impulse

Unfortunately, adjectives fall short when attempting to communicate very specific physics concepts and mathematics is required.....

Impulse is the integral of a force with respect to time.

A small force applied for a long time can produce the same momentum change as a large force applied briefly. But you will observe a different sensation.

What's really amazing is that our physical senses can distinguish between similar events that vary on the scale of miliseconds.

o Unforgiven o
March 21, 2011, 10:27 AM
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?

No, there is such thing as "inherently more accurate", it all comes down to consistency.

So if rifle XX had 1 inch of muzzle rise and rifle YY had 5 inches of muzzle rise, assuming perfect consistency by the shooter and all other variables equal they would both be just as accurate.

Of course, what I just said is not in fact accuracy but precision which warrants another thread all to itself.
(I only jest, there are enough of those threads already)

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