The Maths of Recoil

Don’t forget get to add in trigger pull in your maths and finger weight.

[QUOTE=Moa Hunter;. In my experience a sub sonic projectile with a given momentum will not kill as quickly as a high velocity smaller projectile with the same momentum despite laws of physics[/QUOTE]


Ever tried a 45/70 shooting subs? They leave a pretty big hole and a quick death , especially using expanding rounds like the new Hornady offering.

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Originally Posted by Moa Hunter

While we have recoil at one end of the firearm and the momentum of the projectile at the other, the effect of the projectile on game is not as simple as the amount of momentum nor is trajectory @Puffin. In my experience a sub sonic projectile with a given momentum will not kill as quickly as a high velocity smaller projectile with the same momentum despite laws of physics

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I shoot a lot of animals with 30 cal sub and projectile choice makes a huge difference in quickness of kills for example the Lehigh Defence controlled fracturing with its petals sharing off in multiple directions resulting in more damage and had a few instance bang flops with them on a hilar shot. Shot a red the other day and only went 15m on a broad side lung shot, they work a lot quicker than a standard mushroom design projectiles.

Muzzle energy generally gives a pretty good indication of overall recoil. So if we take two identical rifles, but different calibres - the one with more muzzle energy should have more recoil.
Now that's out of the way, the cartridges ability to rapidly accelerate the rifle (recoil) can be reduced by making the rifle heavier, and/or with the use of a muzzle brake.

Now we have arrived at a base amount of recoil that is directly related to the muzzle energy and firearm weight, (with potentially a muzzle brake thrown in as a curve ball) - how that recoil is transferred to the shooter can be manipulated via stock design, fancy recoil pads and other technologies.

https://www.jbmballistics.com/cgi-bin/jbmrecoil-5.1.cgi

I have spent a while playing around with this calculator, which has powder weight as one of the fields you enter.

For example
7Lb Rifle, 165gr projectile, 2800fps MV, 41gr charge = Recoil Velocity:13.5 ft/s Recoil Energy:19.9 ft-lbs Recoil Impulse:2.9 lb-s

If you somehow managed to achieve the same MV with a 30gr charge (with all else being the same) your numbers would be: Recoil Velocity:12.5 ft/s Recoil Energy:16.9 ft-lbs Recoil Impulse:2.7 lb-s

Not an insignificant difference.

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Originally Posted by tikka

I shoot a lot of animals with 30 cal sub and projectile choice makes a huge difference in quickness of kills for example the Lehigh Defence controlled fracturing with its petals sharing off in multiple directions resulting in more damage and had a few instance bang flops with them on a hilar shot. Shot a red the other day and only went 15m on a broad side lung shot, they work a lot quicker than a standard mushroom design projectiles.

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I reckon subsonic .22lr is better on possums than high velocity...almost like it keeps all its energy inside animal and helps it fall out of tree Vs through n through and possum hangs up.....between the glowing red bits it matters not a hoot,but chest shots ,the subsonics win.

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Originally Posted by SixtyTen

https://www.jbmballistics.com/cgi-bin/jbmrecoil-5.1.cgi

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The jbm calculator is using an exit velocity of 4700ft/sec to calculate the contribution of the propellant.
I believe this was also the figure given historically in Sierra handbooks.

Bit suprised bore diameter has not been mentioned ie same weight projectiles but different calibre in relation to recoil.