Gun Recoil

[Roboss]

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 ?

[lysander]

Drop in the numbers and see for yourself.

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

[AndyLate]

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

[lysander]

The Russian military charge weight is between 22 to 23 grains to meet ballistic requirements.

[AndyLate]

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

[markm]

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]

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]

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.

[AndyLate]

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

[MegademiC]

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