Recoil Energy

[pat fulghum]

Today's daily bulletin article about recoil peaked my interest today.

That article shows a 6mmBR produces 6.23 ft-lb ... I thought that was a bit high...

If you use the online recoil calculator at www.shooterscalculator.com/recoil-calculator.php the only way I was able to get 6.23 Ft-lb with 105 gr was with 30 gr powder, and 2800 fps, but with a 10 pound gun.

So if I use a 21# gun (F-Open) I get...

6mm BRA - 105 gr bullet, 31 gr Powder, at 3025 fps - 3.22 ft-lb
6x47 - 105gr bullet, 41 gr Powder, 3200 fps - 4.22 ft-lb
6.5.x47 - 130 gr bullet, 41 gr Power, at 2900 fps - 4.88 ft-lb
Win .284 - 180 gr bullet, 55 gr Powder at 2820 fps - 8.83 ft-lb

My 284 sure feels like 3x the recoil of my 6mm.

I would be curious what other people's load produce.

 

[Twitchy]

Using my 16.2 pound .223 FTR rifle I get:

1.62 (lbs.sec) Recoil Impulse
3.22 (fps) Recoil Velocity
2.62 (ft.lbf) Recoil Energy

That's with a 90g VLD going 2730fps with 24g of Varget.

 

[Dos XX]

 

[6ShotsOr5?]

24” Savage BA 110 Stealth .338 Lapua Mag with PRS stock, Spuhr mount, ATACR 5x25-56 and Harris bipod ~16.7 pounds pushing 300 gr Bergers at 2691 fps. It’s factory ammo from Hunting Shack but using Berger’s reloading data to get that velocity from my 24” barrel it must be with ~ 89 gr Retumbo or 89.5 gr VIHT N570. BUT I have a Fat Bastard on it so it probably feels like about half of what’s calculated — never have shot it without it. The brake gives a pretty large blast, needs a suppressor.

 

[dcali]

I did a brief study fo this a while back and came up with a chart that describes recoil energy under a wide range of inputs. The numbers in the legend are bullet weight, and this is for a 16 pound rifle. Charge weights were reasonable estimates, and the SAAMI calculation method was used.

 

[6ShotsOr5?]

I did a brief study fo this a while back and came up with a chart that describes recoil energy under a wide range of inputs. The numbers in the legend are bullet weight, and this is for a 16 pound rifle. Charge weights were reasonable estimates, and the SAAMI calculation method was used.View attachment 1048574

Nice chart. I notice the calculator has charge weight but the chart does not. Seems like charge weight should be a small factor overall compared to the muzzle velocity, rifle mass, and projectile mass. I guess maybe charge weight is used for something to do with the mass of gases being expelled from the barrel?

 

[dcali]

Nice chart. I notice the calculator has charge weight but the chart does not. Seems like charge weight should be a small factor overall compared to the muzzle velocity, rifle mass, and projectile mass. I guess maybe charge weight is used for something to do with the mass of gases being expelled from the barrel?

The charge weight matters a lot. The context of that chart was that I wanted to be able to quickly estimate the tradeoffs between cartridges - ballistics vs recoil. Since there is no single charge weight for a given bullet weight (it depends on which powder, and what case), what I did was to look at typical cartridges for each bullet weight, and I fit a curve through that data. That curve was used as the assumed charge weight. So the heavy bullets are assuming higher charge weights. It's not super precise, but it works well for my intended use.

For example, I can tell that adding 300fps to a 6mm will barely be noticeable. But doing the same thing to a .338 will cause a substantial increase in recoil.

 

[dgeesaman]

Nice chart. I notice the calculator has charge weight but the chart does not. Seems like charge weight should be a small factor overall compared to the muzzle velocity, rifle mass, and projectile mass. I guess maybe charge weight is used for something to do with the mass of gases being expelled from the barrel?

Yes, it's part of the energy balance.

http://www.saami.org/pubresources/GunRecoilFormulae.pdf

 

[dcali]

Mathematically speaking the (weight of gun x velocity of gun) = (weight of charge x velocity of charge) + (weight of bullet x velocity of bullet).

The SAAMI method (which was first published in the Textbook of Small Arms by the Brits in 1929) assumes that the gasses are moving at 1.75 times the speed of the bullet, so they are a substantial part of the momentum. You can see the gases outpacing the bullets in pictures muzzle blasts, and it's been experimentally verified as a pretty reasonable assumption.

Take a 308 firing a 180 grain bullet at 2600 fps with a 40 grain powder charge:

The bullet momentum is 180*2600 = 468,000 gr-fps
The powder momentum is 40 * 2600 * 1.75 = 182,000 gr-fps.

The powder accounts for about 28% of the recoil momentum in that case.

Incidentally, this is why muzzle brakes don't do squat to a .45-70, and they are extremely effective on a .22-250 - a much larger part of the recoil is gas related in the .22-250, whereas it's mostly bullet on the .45-70.

 

[6ShotsOr5?]

Mathematically speaking the (weight of gun x velocity of gun) = (weight of charge x velocity of charge) + (weight of bullet x velocity of bullet).

The SAAMI method (which was first published in the Textbook of Small Arms by the Brits in 1929) assumes that the gasses are moving at 1.75 times the speed of the bullet, so they are a substantial part of the momentum. You can see the gases outpacing the bullets in pictures muzzle blasts, and it's been experimentally verified as a pretty reasonable assumption.

Take a 308 firing a 180 grain bullet at 2600 fps with a 40 grain powder charge:

The bullet momentum is 180*2600 = 468,000 gr-fps
The powder momentum is 40 * 2600 * 1.75 = 182,000 gr-fps.

The powder accounts for about 28% of the recoil momentum in that case.

Incidentally, this is why muzzle brakes don't do squat to a .45-70, and they are extremely effective on a .22-250 - a much larger part of the recoil is gas related in the .22-250, whereas it's mostly bullet on the .45-70.

The observation that muzzle brake effectiveness depends on the cartridge is interesting. Cal did some nice tests on a lot of muzzle brakes for precisionrifleblog, but we have to be careful about extrapolating those percent recoil reduction results to loads that are very different (slow heavy bullet loads vs fast light bullet loads). Thanks for explaining that.

 

[dcali]

I would think that in general you can expect a brake that works well on one cartridge to work well on another (within reason). You basically have the powder momentum to work with. The brake’s job is to efficiently redirect that momentum to the side so you don’t feel it. Large brakes with lots of surface area tend to do a good job, but that’s an incredibly complex topic.

 

[dellet]

Another factor that is rarely available in calculators, is powder burn rate. Charge weight is calculated, but what happens when you have two loads and the only difference is peak and muzzle pressures. Quickload has a built in recoil calculator that will compare these, making comparisons of powder choice possible.

Muzzle pressure, translates into a gas force pushing back as the bullet exits.

These were the loads I used as an experiment when I posed a question concerning how burn rates influenced recoil.

“As a refresher the load is 45-70 with a 325 grn bullet at 2000 fps. Charge weight was 40 grains of 5744 and 4100. The numbers below are predicted.

4100
peak press. 41,500
Muzzle press. 3095
Velocity 2030
Muzzle gas force 500
Peak recoil force 6706

5744
Peak press. 37232
Muzzle press. 3711
Velocity 2029
Muzzle gas force 600
Peak recoil force 6016

Since muzzle pressure and the gas force generated on bullet exit is a big factor of recoil, it makes sense that these numbers are a reasonable indicator of felt recoil.

Real world results needed to be judged by feel, which is subjective. For that I simply shot 10 rounds alternating powders. The velocity spread was 30fps, probably a but higher than actual since it was off hand. There was definitely a difference in my ability to control the rifle and felt recoil, with the edge going to the faster powder with less muzzle pressure and gas force, 4100“

http://forum.accurateshooter.com/th...how-do-you-predict-or-measure-effect.3942898/

 

[dcali]

Yes, if you plot recoil force vs time, you’ll see that different powders and rifles yield different results that can have a meaningful impact on felt recoil. The simplest example is a pad on the butt plate. The high level calculations tell you how much recoil you are dealing with. The more detailed calculations like quick load show you more information about how it *might* feel. If the energy is spread out more over time, it’s less annoying. Peak force may or may not be a good indicator. It really depends on the shape of the force curve. At some point it comes down to a subjective judgement, but calculations of either type can be a big help in guiding decisions as you put a rife together or select ammunition.

 

[Zero333]

I have a 17.6 lb tactical/target 243win with a big brake on the muzzle.

Recoil is non-existent.

On the other hand, I got a 7.6 pound 300winmag shooting 190's at 3,100 fps. Recoil's like a bucking bronco.

 

[SteveOak]

Mathematically speaking the (weight of gun x velocity of gun) = (weight of charge x velocity of charge) + (weight of bullet x velocity of bullet).

The SAAMI method (which was first published in the Textbook of Small Arms by the Brits in 1929) assumes that the gasses are moving at 1.75 times the speed of the bullet, so they are a substantial part of the momentum.

But gasses have little masses.

Couldn't help myself.

Yes, if you plot recoil force vs time, you’ll see that different powders and rifles yield different results that can have a meaningful impact on felt recoil. The simplest example is a pad on the butt plate. The high level calculations tell you how much recoil you are dealing with. The more detailed calculations like quick load show you more information about how it *might* feel. If the energy is spread out more over time, it’s less annoying. Peak force may or may not be a good indicator. It really depends on the shape of the force curve. At some point it comes down to a subjective judgement, but calculations of either type can be a big help in guiding decisions as you put a rife together or select ammunition.

I was recently developing a load for 115gr DTAC in a 6BR. I started with Varget but changed to VV N150. The recoil, while similar if not identical in force (same bullet, same velocity), is appreciably less abrupt.

 

[Ray B]

Prior to the bullet and gases exiting the barrel the rifle/shotgun is a closed system. That means that movement within the system will remain in balance. When the cartridge is in the chamber there will be a specific balance point for the rifle. When the cartridge is fired the powder turns into gas but the mass remains the same. The bullet moves through the barrel with the gas behind it. At the point the bullet is just about to break the seal by exiting the barrel the system is still closed but now the bullet and gas have moved. this results in a change in the balance point of the rifle. So if you have a 100 grain bullet and 40 gains of powder, the bullet will have moved from the throat to the muzzle and the powder, now in gas form will be evenly distributed from the base of the cartridge to the base of the bullet. the change in balance point of the rifle is similar to the change in a balance beam scale when the weight is moved along the beam. If the rifle were setting on a friction free surface and its position marked, the rifle would move back the amount to maintain balance, from that marked position. the resulting change may seem inconsequential since in most cases it would be mere hundredths of an inch, however it occurs in the time it takes the bullet to move through the bore. For the example, using the rate of acceleration as a constant, if the muzzle velocity is 3000 fps, then the average velocity during its acceleration is 1500 fps. With an expansion distance (base of bullet in cartridge to muzzle) of 2', the time in bore would be one and a third thousandths of a second. In addition to the rifle wanting to move back to its new balance point there are two quantities that get the shooters attention. the first is that the rifle didn't just move to its new position and stop- in the move it gained momentum which it will continue to have until something (your shoulder) absorbs that momentum, and second, when the bullet left the barrel the pressure of the gases would cause the jet propulsion effect which would cause additional push on the back of the rifle, adding to what the shoulder was absorbing.

So to get back to the original question of why would one rifle seem to have more recoil than another cartridge of similar ballistics- there are two issues: how much movement and time the rifle has during the course of firing, both before and after the exiting of the bullet, and secondly how is that movement absorbed by the shooter.