View Full Version : Gun Recoil
Hi, new guy here. I was wondering what exactly is M4s recoil energy with a 62 grain bullet? Google gives me some different answers. 3 foot pounds, 4.5 foot pounds and just over 5 foot pounds.
Also how much bigger is the recoil of 6x45mm 70 grain bullet at 3000FPS ?
Drop in the numbers and see for yourself. (http://www.shooterscalculator.com/recoil-calculator.php)
For an M4:
Rifle wt: 6.5 to 7.5 pounds
Bullet wt 62 gr (M855)
Bullet velocity: 2850 fps
Powder Charge wt: 25 gr
Hi, new guy here. I was wondering what exactly is M4s recoil energy with a 62 grain bullet? Google gives me some different answers. 3 foot pounds, 4.5 foot pounds and just over 5 foot pounds.
Also how much bigger is the recoil of 6x45mm 70 grain bullet at 3000FPS ?
The recoil of a 6x45 70 grain bullet is effectively identical to a 5.56x45 69 grain bullet. A link was provided for you to run the numbers but you really need to know the weight of the powder charge as well.
Andy
The Russian military charge weight is between 22 to 23 grains to meet ballistic requirements.
6x45 is a wildcat cartridge - .223/5.56 necked up to 6mm.
It is like asking about the recoil difference between 150 gr 30-06 and 150 gr 280 Rem.
Andy
Wouldn't recoil energy vary wildly depending on gassing and buffer system? I mean... I've shot over gassed carbines that will impulse way harder than a correctly gassed gun.
Steve Shannon
01-30-21, 11:36
Wouldn't recoil energy vary wildly depending on gassing and buffer system? I mean... I've shot over gassed carbines that will impulse way harder than a correctly gassed gun.
It depends on what you call recoil. Recoil energy must be equal to the kinetic energy of everything that emerges from the muzzle. But, how that energy is delivered determines how you perceive it.
A better way to analyze it would be conservation of momentum and understanding that the change in momentum over time at the interface between the firearm and the shooter, which is called impulse, results in vastly different perception of “recoil”.
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Dr. Bullseye
01-30-21, 12:54
Hi, new guy here. I was wondering what exactly is M4s recoil energy with a 62 grain bullet? Google gives me some different answers. 3 foot pounds, 4.5 foot pounds and just over 5 foot pounds.
Also how much bigger is the recoil of 6x45mm 70 grain bullet at 3000FPS ?
Would this not depend on the velocity the bullet left the barrel (among other factors)? And if so, you get into a bunch more variables.
5.56 will drive a 69 gr bullet at 3000 fps according to Ramshot's load data. I am going to go out on a limb and say the 6x45 will require a grain more powder to reach the same velocity with a 70 gr bullet. Call it 26 grains for the 5.56 and 27 for the 6mm.
Assuming a 7.5 lb rifle, the 5.56 recoil energy is 4.8 fpe, the 6x45 is 5.3 fpe.
Compare that to a 7lb 308 Win that generates 21 fpe or a hot loaded 45-70 Guide Gun at 40+ fpe and you can understand why I say there is no practical difference between the 5.56x45 and 6x45 recoil.
Andy
5.56 will drive a 69 gr bullet at 3000 fps according to Ramshot's load data. I am going to go out on a limb and say the 6x45 will require a grain more powder to reach the same velocity with a 70 gr bullet. Call it 26 grains for the 5.56 and 27 for the 6mm.
Assuming a 7.5 lb rifle, the 5.56 recoil energy is 4.8 fpe, the 6x45 is 5.3 fpe.
Compare that to a 7lb 308 Win that generates 21 fpe or a hot loaded 45-70 Guide Gun at 40+ fpe and you can understand why I say there is no practical difference between the 5.56x45 and 6x45 recoil.
Andy
Yeah, raw energy numbers are purely academic with no real application
Gatorgrizz27
01-31-21, 07:08
Wouldn't recoil energy vary wildly depending on gassing and buffer system? I mean... I've shot over gassed carbines that will impulse way harder than a correctly gassed gun.
Correct IMO. I have a .223 bolt gun that weighs the same or less than my AR’s and the “felt recoil” is substantially less than any of them. The “felt recoil” from most AR’s is more a result of 1 lb of steel slamming to a stop into your shoulder than from propelling the 55 gr bullet forward.
Yes, I know all about the physics, that it can’t actually create more energy than the cartridge firing produces, etc, but that’s not how it comes across.
Recoil energy and felt recoil are different. If you bungee cord both my 18" 223 bolt rifle and my 18" Rifle gas AR on a little red wagon and fire the same round in each, the wagon will move the same distance.
Shooting each at the range feels entirely different due to a number of factors. Generally speaking, semi autos shoot "softer" because the recoil impulse is spread over a longer period.
A well set-up AR shoots "softer" because the cyclic rate is slower and recoil is, again, spread over a longer period. An overgassed AR with a too-light buffer and weak recoil spring has a shorter recoil cycle and "harsher" recoil.
The OP asked about recoil for a 6x45 70 gr @ 3000 fps compared to a M4 (I assume 5.56). If the OP shoots the 6x45 and a 5.56 (69 gr @ 3000 fps) from a similar firearm, there is no practical difference.
Andy
Recoil energy and felt recoil are different. If you bungee cord both my 18" 223 bolt rifle and my 18" Rifle gas AR on a little red wagon and fire the same round in each, the wagon will move the same distance.
Andy
I don't think this can be true because a spring will store some of that energy ("stealing it from the round") and then returns it back to the BCG going in the fwd direction. The energy absorbed by the spring and then returned back to a impact force as BCG slams into battery in opposite direction would cause the wagon to travel a lesser distance.
A bolt will always put more energy into the bullet vs a semi-auto? Why? Because the very point in time the back of the bullet passes the gas port there will be a PSI "drop" behind the bullet, thus a little energy is now in the gas system.
The diff may not be significant, but the two are different.
Well I can say for sure that my first AR upper (a RRA overgassed 16” carbine system HBAR) had WAY more felt recoil than the lightweight 14.5” BCM middy that replaced it, despite the vast difference in weight, both shooting 55 gr. Wolf gold.
And when I dialed in the adjustable gas block on my 12” 6.5 Grendel, I did feel a difference from wide open to dialed in.
No difference in loads. Calculators are good for comparing theoretical differences in calibers, but for felt recoil, that’s got more to do with the rifle. A Limbsaver pad can reduce felt recoil, even if it’s just spreading the same energy over a longer period.
Failure2Stop
02-01-21, 09:18
There's a lot more to recoil than can be quantified with a calculator.
Here's how it's really done:
https://www.youtube.com/watch?v=NiTGEBgcKqQ
]I don't think this can be true because a spring will store some of that energy ("stealing it from the round") and then returns it back to the BCG going in the fwd direction. The energy absorbed by the spring and then returned back to a impact force as BCG slams into battery in opposite direction would cause the wagon to travel a lesser distance.
A bolt will always put more energy into the bullet vs a semi-auto? Why? Because the very point in time the back of the bullet passes the gas port there will be a PSI "drop" behind the bullet, thus a little energy is now in the gas system.
The diff may not be significant, but the two are different.
No.
1) The spring pushes in both directions, it pushed the bolt forward, and the rest of the gun backwards. So, it does not "steal energy", it just borrows it, and returns it at a later time.
2) Where does the gas go? It goes into the cylinder and pushed the piston rearward into your shoulder via a spring.
The thought experiment described by Andy has been carried out many times and the results are always the same, the little wagon rolls back the same distance. It's been done with wagons, sleds, suspending them on strings, dropping them, anyway you can imagine. And, it always agrees with the calculations from the laws of conservation of momentum and conservation of energy.
People that think that recoil is different for different operating mechanisms are the same ones that think that a blow-forward gun is a reasonable idea.
Perceived recoil =/= recoil
How is a bcg slamming fwd into battery any different than the energy of round blast hitting a muzzle brake?
In both cases some of the blast energy slams into the rifle barrel with a energy vector 180deg from recoil.
Sled tests of various brakes show us how the brakes reduce the recoil energy.
Steve Shannon
02-01-21, 13:37
How is a bcg slamming fwd into battery any different than the energy of round blast hitting a muzzle brake?
In both cases some of the blast energy slams into the rifle barrel with a energy vector 180deg from recoil.
Sled tests of various brakes show us how the brakes reduce the recoil energy.
A muzzle brake redirects mass which would otherwise have been forward momentum and which would have resulted in recoil if not redirected.
The BCG slamming backwards and then forward displaces the recoil in time but doesn’t increase or decrease it.
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How is a bcg slamming fwd into battery any different than the energy of round blast hitting a muzzle brake?
In both cases some of the blast energy slams into the rifle barrel with a energy vector 180deg from recoil.
Sled tests of various brakes show us how the brakes reduce the recoil energy.
Muzzle break reduces recoil because the recoil from the gas itself is reduced. It is 2 vectors (left and right) both 90dregrees to the recoil vector, so they cancel each other out
Everything about the bcg is inline with the bore. All the energy that the bcg slams home with has been put in the recoil direction the entire cycle time.
If you shoot an open bolt gun, you'd get it. The gun recoil before the round fires, resulting in high shots
Muzzle break reduces recoil because the recoil from the gas itself is reduced. It is 2 vectors (left and right) both 90dregrees to the recoil vector, so they cancel each other out
Everything about the bcg is inline with the bore. All the energy that the bcg slams home with has been put in the recoil direction the entire cycle time.
If you shoot an open bolt gun, you'd get it. The gun recoil before the round fires, resulting in high shots
Brakes allow the gas to change direction by way of resistance. The bore is say X axis. When the gas turns there is XY components of the forces, the Y's cancel but the X's on left and right side add up, and in this case it's all in same direction, thus pushing the barrel fwd some.
As far as the red wagon (sled) tests, it's not possible for two rifles of varying mass to move the same distance when using the exact same rounds. It's a MV=MV conservation equation.
A sliding BCG picks up some recoil energy, which is then returned back in opposite direction (identical to a brake). The timing of the events is obviously spread out over time.
This one is a good explanation of it.
https://www.chuckhawks.com/rifle_recoil.htm
After thinking about it, the gas used to cycle the bcg vents out the side, but most of the energy was transferred to the bcg.
The forward energy of the bcg was transferred to the shooter during the forward stroke as I mentioned above. The net recoil is the same.
Another example, hit the bolt release on a locked back rifle. The gun recoil, then gets pulled forward upon slamming home resulting in zero net recoil.
After thinking about it, the gas used to cycle the bcg vents out the side, but most of the energy was transferred to the bcg.
The forward energy of the bcg was transferred to the shooter during the forward stroke as I mentioned above. The net recoil is the same.
Another example, hit the bolt release on a locked back rifle. The gun recoil, then gets pulled forward upon slamming home resulting in zero net recoil.
If you lay down and put 5 bricks on your chest, is there any energy entering your body? There's a force you feel, but no energy transfer.
If you absorbed the BCG energy then the spring would never compress or decompress.
If you lay down and put 5 bricks on your chest, is there any energy entering your body? There's a force you feel, but no energy transfer.
If you absorbed the BCG energy then the spring would never compress or decompress.
As the spring decompresses, the gun is pushed back into your shoulder.
rcoodyar15
02-15-21, 06:33
The recoil of any .223 is negligible.
You can feel a little recoil in a lightweight 6.5 grendel
When you get to .308 then you can talk about recoil. Biggest variable is the weight of the gun
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