Powder weight and recoil

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Quiet

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I'm wondering if powder weight has an effect on recoil.
Clearly, different weights of the same powder, producing different velocities will produce different recoil, but I am talking about 2 different powders, with different charge weights, loaded to move a bullet at the same velocity.

For instance, from my Lyman manual:
In a .308 Winchester, 39 grains of RX7 under a 150 grain bullet produces a velocity of 2739 fps, while 50 grains of H-414 pushes the same bullet to 2733 fps.

The first load is ejecting a total of 189gr of "stuff" out of the barrel while the second load is sending out 200gr.

Accuracy considerations aside, if one was working towards a light recoiling cartridge, would it be best to pick the most efficient powder on the list?
 
I think you answered your own question: the weight of the powder is added to the weight of the bullet, so at the same muzzle velocity with the same weight bullets, the heavier powder load produces the heaviest recoil. In the example you gave, I doubt the difference in recoil would be noticeable. The H414 load would produce a lower peak pressure, but a higher muzzle pressure, hence a louder report.

The most important factor remains accuracy.
 
Andy said:
The H414 load would produce a lower peak pressure, but a higher muzzle pressure, hence a louder report.
Click to expand...

That is interesting. I believe we process muzzle blast as a part of the recoil (mentally), so that may support the theory that the RX7 load recoils less. The fact that the ejecta weighs less means the load will indeed produce less recoil with equal velocity. Just my 2 pennies.
 
This becomes very obvious with muzzle loading firearms (and black powder cartridge guns). A .600 ball with 70 grs of black powder does not have much recoil but up the powder charge to 100+ grs and the recoil gets stiff.
 
Quiet said:
Accuracy considerations aside, if one was working towards a light recoiling cartridge, would it be best to pick the most efficient powder on the list?
Click to expand...

Talking about efficiency of powder ( a little off topic from your recoil question);
if you look at the 2 loads you have listed, from an economic stand point, I would choose the 39gr over the other charge as it will give you more rounds per pound. Accuracy aside, as you said.
 
Quiet said:
I'm wondering if powder weight has an effect on recoil.
Clearly, different weights of the same powder, producing different velocities will produce different recoil, but I am talking about 2 different powders, with different charge weights, loaded to move a bullet at the same velocity.

For instance, from my Lyman manual:
In a .308 Winchester, 39 grains of RX7 under a 150 grain bullet produces a velocity of 2739 fps, while 50 grains of H-414 pushes the same bullet to 2733 fps.

The first load is ejecting a total of 189gr of "stuff" out of the barrel while the second load is sending out 200gr.

Accuracy considerations aside, if one was working towards a light recoiling cartridge, would it be best to pick the most efficient powder on the list?
Click to expand...

Yes - choose the "most efficient" powder, as you describe it. It will produce the highest pressure, for that velocity (so long as the pressure is still safe, that's fine). Because of the higher pressure reached, it will also be more likely to be the most uniform, and has a good chance of being the most accurate to.

As you correctly note, there is 189 grains of mass being ejected in case #1, and 200 grains ejected in case #1. There's a further twist to this.... and that is that the powder gas is ejected at a speed that is a lot higher than the bullet. For typical rifle cartridges, Hatcher's Notebook suggests that 5,000fps is a pretty good estimate of the mean speed of the powder gas.

So the recoil, expressed in the wonderfully rational (not! ;-) units of "fps*grains", is:

39 Rx7 / 150@2739:
39 grains powder * 5000fps + 150 grains bullet * 2739fps = 605,850 fps-grains

50 H414 / 150@2733:
50 grains powder * 5000fps + 150 grains bullet * 2733fps = 659,950 fps-grains (9% more recoil)

So on a strictly mechanical basis, you would expect load#2 to produce 9% more recoil. In reality you might perceive even more than this, because of two more factors:
- firstly, the muzzle exit pressure of the 50 grain charge will likely be higher. More pressure at muzzle causes a bigger bang, which increases our perception of recoil
- unless the powder has a lot of good flash suppressants in it, you are more likely to get muzzle flash from the higher pressure gun gas in load#2
 
This is the principle that muzzle brakes operate on - redirecting the powder portion of the recoil in a different direction, thus eliminating it. If it's redirected backwards (i.e. more than 90* from the axis of the bullet), it can even offset the recoil of the bullet to some degree.
 
A very good thread on a topic rarely covered here, that covers several principles of internal ballistics.
 
Most recoil calculators add half of the powder weight to the bullet weight. That's fine as an approximation, but you can't take subjective out of recoil.

Heres a couple of examples:

In one of my .300 Wins a stiff load of H1000 will get it barking and bellering with 180s. 10 grains less of 4350 comes in 150fps or so slower in velocity and is a sedate little thing that seems like it couldn't blow the dust off the bench. That little difference in charge weight and velocity reduces recoil all out of proportion to what seems likely. Back the H1000 load off until velocities are close and it'll still kick more. I like my H1000 and will continue useing it but the difference is pretty obvious if your's is kicking you around.

A Cooper 30-06 that I'm playing with likes 165s. Maximum loads of H4350, RL19 and RL22 are supposed to run circles around my 4064 and Varget loads but according to the chronogragh aren't actually doing it. In fact, they are lucky to match the speeds. Recoil is noticeably more while burning more powder to go slower. Luckily they make up for it by shooting worse and heating up the barrel faster.:rolleyes:

My Savage muzzleloaders with 43 -44 grains of SR4759 will absolutely destroy the velocities that the same guns will produce with 3 pyrodex pellets.(150 grains equilent) The Pyrodex loads produce African style recoil, while a thimble full of smokeless barely moves the gun around. You can even hear the bolt clank in recoil.
 
prosper said:
because it exits the muzzle at twice the speed of the bullet
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Some of it does, some of it got to the muzzle at exactly the same time as the bullet or it would have passed it. Some will reach the speed of expanding gas, and the rest is in between somewhere depending on how much time it had to accelerate. At least that's how I understand it.
 
consider that the barrel is pressurized at several thousand PSI. As soon as that bullet's out of the way, the gas is going to accelerate out of there like a bat out of hell. This is why the 'mean' gas velocity is listed as 5,000fps. Some will be less, some more, but it will average out.
 
It does make more sense to me useing mean. In any case I know the felt recoil goes up rapidly with high charges of slow burning powder, I'm just working on understanding the math now
 
Prosper has got it.

At the moment of bullet exit, the gas at the breech face has a speed of zero, the gas at the base of bullet has the same speed as the bullet. And, the whole barrel full of gas is still under a fair bit of pressure (on the order of 10,000 psi). Once the bullet leaves, that 10,000psi gas "blows down", and accelerates from those starting conditions.

The "5000-6000fps mean effective velocity" is basically just the weighted average speed of the gun gas.

Keep an eye out for high speed photographs of a bullet just after it exits the muzzle (say, half an inch to two inches from the crown). You can see how quickly the gun gas, now no longer restrained by the bullet in the bore, accelerates and passes the bullet. You can usually see shockwaves produced by the gas, indicating its progress. Pretty neat photos to study!
 
rnbra-shooter said:
Prosper has got it.

At the moment of bullet exit, the gas at the breech face has a speed of zero, the gas at the base of bullet has the same speed as the bullet. And, the whole barrel full of gas is still under a fair bit of pressure (on the order of 10,000 psi). Once the bullet leaves, that 10,000psi gas "blows down", and accelerates from those starting conditions.

The "5000-6000fps mean effective velocity" is basically just the weighted average speed of the gun gas.

Keep an eye out for high speed photographs of a bullet just after it exits the muzzle (say, half an inch to two inches from the crown). You can see how quickly the gun gas, now no longer restrained by the bullet in the bore, accelerates and passes the bullet. You can usually see shockwaves produced by the gas, indicating its progress. Pretty neat photos to study!
Click to expand...

Just one of the reasons why you want to have a well polished crown as you want those gasses to be evenly distributed around the bullet upon exit.

Take Care

Bob
 
I have owned many different calibers in hunting rifles. I am not very recoil tolerant. I think it may have something to do with the shape of my shoulders. Anyway, all the technical points considered, I use a 270 win for hunting .I now use a 110gr Barnes TTSX loaded a few grs under published max IMR4350. This does everything you could wish for on white tails.
Fast,flat shootting, bullet holds together,dead dear on the spot.
 
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