Ok guys, the curiosity has the better of me and I need the help of a math or physics expert out there.

Is there a formula for calculating recoil in various rifles that takes into account gun weight, bullet velocity, bullet weight, etc?

I ask because I have a .500 NE double that weighs about 10 lbs 3 oz, and our .577 NE will be arriving soon that will weigh around 14 lbs.

For the .500, we found that 94 grains of RL-15 work well. The recoil is very managable for me.

The .577 NE will be regulated for 115 grains of RL-15.

I'm curious if there is a way to calculate the recoil of both rifles, because I THINK (scary, huh) that the recoil of the .577 MIGHT be close to that of my .500 since it will weigh four pounds heavier.

Any thoughts on this?

There is but I cheat and use one of the online calculators.

There are several -- just search "recoil calculator" or try the one linked above. I have not used it before so caveat emptor,

Recoil velocity and recoil energy are the two most common things you want to look at. Recoil velocity is the sum of bullet velocity and powder velocity, in pounds, divided by the weight of your rifle. There are 7000 grains per pound so you divide the weight of the bullet in grains by 7000 and multiply by its velocity is feet per second. Second, you divide the weight of the powder in grains by 7000 and multiply by 4700 fps, the estimated average velocity of most rifle powders. Sum these two numbers. Divide this sum by the weight of your rifle in pounds and you have recoil velocity in feet per second. Recoil energy calculation requires squaring the sum you calculated and dividing by 64.348 (1/2 times the earth's gravitational constant, roughly 32.174 feet per second per second)and then dividing again by your rifle's weight, giving you an answer in foot-pounds.

376steyer:

I took physics in college, but I feel like a retard reading your post

Thanks for the info. I will run the numbers and see what I get.

Danke,

quote:

Originally posted by 376steyr:
Recoil velocity and recoil energy are the two most common things you want to look at. Recoil velocity is the sum of bullet velocity and powder velocity, in pounds, divided by the weight of your rifle.

Velocity is a measure of speed and direction.. often people use the word simply for speed. Speed is measured in distance per unit time (ie ft/sec). It isn't pounds.

The units of measure of "impulse" on that web site are a little odd. Impulse is a measure of momentum, usually lb-secs.

The formula you describe looks sort of like the momentum of the projectile + momentum of the powder (= total momentum transferred to the rifle) divided by the mass of the rifle, to get velocity. Momentum is mass times velocity.

English units are a little weird. You can use lbs as mass, but need to talk about another unit of force (multiply by acceleration due to gravity to get weight); or you can use lbs as weight, and divide by gravity to get slugs. I grew up to use the slugs system. In that case, to get velocity from lbs-sec, you have to divide by MASS, which is in slugs = weight in lbs / g (g = 32.2 ft/sec^2).

The velocity of the powder flash gas as 4,700 ft/sec is frequently quoted...

quote:

There are 7000 grains per pound so you divide the weight of the bullet in grains by 7000 and multiply by its velocity is feet per second. Second, you divide the weight of the powder in grains by 7000 and multiply by 4700 fps, the estimated average velocity of most rifle powders. Sum these two numbers. Divide this sum by the weight of your rifle in pounds and you have recoil velocity in feet per second. Recoil energy calculation requires squaring the sum you calculated and dividing by 64.348 (1/2 times the earth's gravitational constant, roughly 32.174 feet per second per second)and then dividing again by your rifle's weight, giving you an answer in foot-pounds.

Dan

I was wondering what number to use for powder velocity. How average is 4700 fps? Extreme spread of typical powders?

I guess one could calculate that knowing the chemical formula of the powder and the amount of air in a case (porosity), etc.

Taylor must have been a smart man.

But the numbers really don't give an idea about recoil. The 470 NE is a strong push, while a 460 Weatherby sells more used rifles than any other.

For recoil, kinetic energy or a Taylor knock out value does not help. We have to get into real physics - the shape of the cartridge, the angle, the powder, the primer....you get the picture.

And a 7 pound rifle will hurt you more than a 9 pound rifle. And then there's the stock design.

If you want to buy a rifle, get a trial period.

I have a 308 that kicks like a mule, and a 50 caliber that is gentle.

My opinion is that there is no program out there to judge recoil. There are too many variables.

If yu shoot it, and you like it, than go for it.

Jim

Paul, here is the on-line calculator I use

http://huntamerica.com/recoil_calculator/

500NE, 10.2lbs, 570gr, 94gr powder, @ 2150fps = 77 ft lbs recoil at 22 fps.

577NE, 14.0lbs, 750gr, 115gr powder, @ 2150fps = 94 ft lbs recoil at 20 fps.

Hog Killer

quote:

Originally posted by Hog Killer:
Paul, here is the on-line calculator I use

http://huntamerica.com/recoil_calculator/

I've used that one too, but linked to one of the many that showed up in a search rather than to the other board, not that there is anything wrong with that.

quote:

Paul, here is the on-line calculator I use

http://huntamerica.com/recoil_calculator/

500NE, 10.2lbs, 570gr, 94gr powder, @ 2150fps = 77 ft lbs recoil at 22 fps.

577NE, 14.0lbs, 750gr, 115gr powder, @ 2150fps = 94 ft lbs recoil at 20 fps.

Hog Killer

Hog:

Thank you kind sir!

I have to remember to pop a few asprin about an hour and then right before I pull the trigger on the .577.

Thanks,

Paul, I hope you are having a nice BIG recoil pad put on that monster.

Charles, that is the only thing from that site that I use. I never go to that forum.

Hog Killer

Just calculated likely recoil for my .600 and assuming the rifle ends up with a 16lb weight then receoil energy computes to 104 ft lbs!!!

I can feel a flinch coming on!!

I just shot my 10 ga turkey gun yesterday for the first time. I was using some 2 1/4 oz loads that were moving somewhere between 1250 and 1300 fps. My shotgun is probably about 10 lbs. I ran the numbers through the online calculators, and it gave me a recoil energy of between 54 and 59 ft lbs, or about the same as a .458 Win Mag shooting a 500 gr bullet at 2150 fps.

Has anyone here actually shot the two side by side? Is the comparison accurate, or are the numbers lying?

analog_peninsula

What the calculators give you is "free recoil", when your making compairisons your (generaly) speaking about "felt recoil". Felt recoil is difficult to quantify, as the design and fit of the stock will have a large infulance on the results.

the ugly number you probably really, really don't want to hear is Recoil Impulse Number. That is the speed at which the recoil impulse impacts on your unworthy shoulder. It's also called "felt recoil". It's why light rifles kick "harder", the rifle moves quicker due to less inertia to overcome. I have a computer program somewhere that formulates that impulse number. I will try to dig it out. It explained why a standard weight 378 Wby hurt more than shooting Elmer Keith's 600NE the same afternoon.

Rich

I doubled my 470 NE the first time I shot it...it was a mite uncomfortable.
The shots were within an inch of each other at 50 paces....the next few kinda spread around a little for some unknown reason...hmmm....

According to Jeffeosso:

10.5 lb rifle + .500 NE + 106 grains IMR4350 = Ouch!

quote:

Originally posted by Will:
I was wondering what number to use for powder velocity. How average is 4700 fps? Extreme spread of typical powders?

I guess one could calculate that knowing the chemical formula of the powder and the amount of air in a case (porosity), etc.

I have seen that number quoted in some reloading manual or other. I can check later when I get home exactly which one. I can only believe it is a rough guestimate.

I have seen more detailed articles describing how powders burn in differently shaped cartridges -- long and skinny or short and fat -- suggesting there's good science behind the idea that short-n-fat cartridges burn powders much more efficiently, and deliver the energy more effectively to the projectile. But given the range of variation due to shape, much less the variation in burn rates for different powders in any particular cartridge, I would have a hard time thinking the 4,700 fps could be more than just a guess designed to try to capture a representative effect of powder burn.

When it comes down to it, 22 ft/sec recoil in a 10 lb gun has to be different from 22 ft/sec in a 5 lb gun. Then there's how the energy is transferred to your body... If its slow enough, more of your body can take the shock; the more rapid it is, the more flexing through your body as the momentum gets transferred -- the difference between jab and shove for same total momentum transfer. There's stock shape, how you hold your rifle... lots of variables.

In the face of all the variations that affect the sensation of recoil, how precise do you have to get about the effect of gas velocity?

Dan

Dan,

It is not that I do not believe the 4700 fps. It is just that I was wondering what all the variables one would have to know to do a rough calculation (just for fun).

Someone along the way must have done the calcs, surely for the military if not for the sporting crowd. There are probably books on calculating flame spread in porous solid propellants, etc.

I would guess that short, fat cases have a quicker flame spread through the whole quantuty of powder and therefore a faster pressure peak, but whether that really makes any differnce in anything I do not know.

I sort of doubt the gunwriters praises usually; those that never met a gun (or new cartridge)they didn't like!

I had fun calculating 2500grain bullets...one whiskey makes me creative

Paul, If I get to shoot your 577, I'm using Keith, Jim, or Jeffe for a recoil pad!

Let me know when you work up some wussy cast loads!

quote:

Originally posted by Rusty:
Paul, If I get to shoot your 577, I'm using Keith, Jim, or Jeffe for a recoil pad!

Let me know when you work up some wussy cast loads!

Rusty, I'll do anything to help out a good friend.

Hog Killer

I think Tailgunner and ID Sharpshooter hit the nail on the head.

Free recoil is only a part of the story. When I (5' 6", 155lb) shoulder and fire a rifle it accelerates differently than if it were hanging on a string. Put another way, the rifle plus my upper body mass moves slower than just the rifle would, and probably differently from how your's would with the same rifle. Recoil energy varies with the square of velocity, but it is that total rifle/body velocity, so the actual amount of energy is less that the calculators show. It is a bit like looking at racing bikes. Bike A may have 3.0 lb/hp and bike B 3.3 lb/hp, but that 10% advantage goes all to hell when you add a 250lb rider.

Add in stock shape, proper(or not) hold, butt area, balance, recoil pad, etc and it really gets murky.

Impulse is the other huge factor. Just how quickly is that energy delivered? Asquare's manual talks a bit about this FWIW. I have some BP and bore rifles that are FAR less horrendous than their numbers would make them appear, even when leaving powder weight out of the equation. Speed and muzzle jump are what make'em brutal to me.

I kind of look at it like Taylor's formula or Foot-Lbs of energy. It useful for comparing load A to B, or rifle A to B, but don't think it means A is 3.21345542 times as good(or bad) as B.

Bob

Rusty and Keith:

You all are welcome to shot that thing whenever we get together. Rusty, you have to shot the full load, just once, to say you've done it. But please, this time, no doubling....

Recoil Formula:

(Wb X Vb) + (Wp X .77143)
Vr= --------
(7000)
----------------------------
Wr

where as:
Vr= Velocity of rifle in "feet per second"
Wr= Weight of rifle in "pounds"
Wb= Weight of bullet in "grains"
Vb= Velocity of bullet in "feet per second"
Wp= Weight of powder in "grains"

Note: .77143 is a factor showing change of powder weight to pounds and a powder gas exit velocity of 5400 fps; 7000 is a factor converting bullet weight in grains to pounds,

Thus----

Recoil energy then equals:

2
(Vr) X (Wr)
Err= ---------------
64.32

Where:

Err= Energy of rifle in recoil in :foot pounds"
Vr= Velocity of rifle in "feet per second"
Wr= Weight of rifle in "pounds"

Note: 64.32 is a gravitational constant

Now you do the math!

quote:

Has anyone here actually shot the two side by side? Is the comparison accurate, or are the numbers lying?

I shoot a Browning BPS 10 ga mag with 2 1\4oz payload Federal Premium. I have also read that the recoil is roughly equal to the 458 Win mag. That's how I knew I could handle a Win model 70 in 416 Rem mag. And also that I could never tolerate those really big bore thumpers. Good luck for those that can, however.

quote:

Originally posted by 577NitroExpress:
Rusty and Keith:

You all are welcome to shot that thing whenever we get together. Rusty, you have to shot the full load, just once, to say you've done it. But please, this time, no doubling....

Paul, just play it safe with Rusty, one loaded round and one primed empty case. That way if he doubles it we have proof and his shoulder stays almost in place.

Hog Killer

Gee that's what I thought! Just load one barrel at a time!