Recoil question

[gamestalker]

Something that has always baffled me is recoil.

When I load 38 special for instance, a 125 gr. XTP loaded with heffty charge of Longshot it will chronograph in the mid 1200 fps range. Shooting through the same revolver (S&W 66) the same bullet in a .357 mag. case with a charge of H110 that produces a similar velocity, will produce a much higher amount of felt recoil, why?

Another example is a .243 loaded with a 105 gr. bullet and a 7mm mag. shooting a 100 gr. bullet at very similar velocities are also two different worlds of recoil. The 7 mag. with the lighter bullet and close to same velocity is painful to shoot in comparison to the .243 win..

I know that there are very different pressures at play here, but I wouldn't think that pressure can have that degree of effect?

 

[rcmodel]

Grains of powder enter into the total projectile mass.

Play with this and put in the powder charges with equal gun weights.
http://www.handloads.com/calc/recoil.asp

You will see it does make a difference, but not a very big one.

I'd say if the .38 kicks as hard as the .357, the guns didn't weigh the same.

If two rifles shooting the same bullet weight at the same velocity, and weighing the same kick differently? One stock fits you better then the other one.


rc

 

[gamestalker]

Thanks for the response RC, but it still doesn't offer sufficient explanation, especially considering the same firearm was used for the 38's and .357's. With two different rifles one can reason why it may be noticably different. And this is also something I've noticed with any wheel guns that will function with specials or magnums. The recoil is always considerably greater with the magnum cartridge, despite very similar or same velocities.

 

[rcmodel]

Only bullet weight, velocity, and powder ejecta are accelerated to create an equal & opposite force, or recoil.

If there is a difference in felt recoil with equal weight bullets at the same velocity in the same gun?

Powder burn rate can change the feel.

And, the slower powder used in the magnum will have more muzzle blast then the faster powder used in the .38.

Lots of folks mistakenly equate increased muzzle blast with more recoil, when in fact, the recoil has to be the same if the velocity is the same.
Newtons Law says so.

rc

 

[kingmt]

The recoil is the muzzle blast. Your rifle is acting like a rocket taking off & into your shoulder. Faster powder burning up before the bullet leaves the barrel won't have as much blast left to push the rifle back. The amount of surface area on the back of the bullet is to small to make a difference once it leaves the barrel that you would ever notice. You are felling the resistance fro the air.

I bet a flogging is coming.

 

[jmr40]

A lot of recoil is actually between the ears. People assume that a certain gun will kick more, and to them it does. It's a magnum, so it must recoil harder.

If two rifles shooting the same bullet weight at the same velocity, and weighing the same kick differently? One stock fits you better then the other one.

True, the stock shape plays a big part in felt recoil, but there are 4 variables to determine recoil. Bullet weight, rifle weight, bullet velocity. You left out the 4th variable, powder weight.

Some chamberings and powder combinations are more efficeint. A 300 WSM can achieve 3200 fps with a 150 gr bullet with as little as 68 gr of powder. A 300 Weatherby Mag. can use as much as 85 gr to achieve the same velocity.

That means 26.6 ft lbs of recoil vs only 22.4, about a 15% increase in recoil to get the same velocity. Assuming both are in 8 lb rifles.

 

[rcmodel]

You left out the 4th variable, powder weight.

I thought for sure that's what I said in the first sentence of post #2??

rc

 

[gamestalker]

Now I understand what you ment by powder mass weight RC. It makes complete sense, and would surely make a noticable difference in what one would feel in comparison to a lighter charged case of faster burning powder.
Thanks
GS

 

[denton]

Recoil starts the moment the bullet starts to move down the barrel. Newton's laws require that if a system is not being acted upon by outside forces, its center of mass will not move. So as the bullet and the gas move down the barrel, the rifle has to move backward so the center of mass of the rifle + bullet + gas remains in the same place.

When the bullet uncorks the barrel, the gas escapes. This is governed by exactly the same principle, and, indeed, is a rocket.

A rifle accelerates at roughly 500X the acceleration of gravity for about a millisecond and a half. During that time, it moves about 1/8". After that, your shoulder takes over and slows it to a stop.

The conventional method for calculating recoil gives a real, physics based number that is practically meaningless. Shooting from the shoulder seriously violates the assumptions of the calculation, and the number that the calculations produces only distantly relates to perceived recoil. What matters in felt recoil is force, as it unfolds over time. What the calculation produces is the sum of the effects of the force, accumulated to the end of the event.

 

[Clark]

When I was a little boy, my father was chief engineer pounding on table tops and designing guns.
I thought my father said that in "Hayes Elements of Ordinance" that the velocity the gas was 1.5 times the velocity of the projectile. But looking at that book right now, the estimation used is that the center of the gas mass has a velocity of 4700 fps.
He designed some small machine guns, but mostly he had hydraulic recoil on bigger guns.
http://www.booksamillion.com/p/Elements-Ordnance/Thomas-J-Hayes/9781432518110

I have been trying to get perceived recoil down on my handguns and long guns.
The optimization seems to be a heavy gun, light bullet, a compliant human interface that allows coupling the recoil energy of the gun into the human spread evenly over area and time.
So a 5 pound shot gun with a needle for a buttstock will spread the recoil over time, but not over area, so it would hurt.
The surface of our skin has nerves just under it that register pain ~ 50 psi.
I have been experimenting with recoil pads.
The superiority of Limb Saver over other pads, like Kick-eez, is dramatic.
I have been experimenting with recoil springs in semi auto pistols.
I realized that not all the bullet and gas momentum goes into slide velocity relative to the frame. Half of it gets lost accelerating the arm and the frame. The pain of semi auto pistols is very non linear. The 50 psi pain threshold is not usually crossed while the recoil spring is being compressed. But if the recoil spring is inadequate, the remainder energy goes into the slide hammering the frame. This remainder acts through a hand -frame interface of flesh that is already compressed. A small change in that remainder can make a big change in perceived pain.
The other problem is noise. A really loud gun can seem like it is kicking harder than it is.