Equating recoil to force or energy doesn't tell the whole picture.

Think of your car - constant acceleration results in a constant force on your body. This will feel like being pressed back in the seat like your weight has increased.

But cars don't accelerate at a constant rate, the rate of acceleration changes, and this is called "jerk" (yes this is the actual technical term). Jerk is what you immediately feel when you press the accelerator or the brake. Jerk is a lot more uncomfortable than constant force/acceleration.

For firerams it is similar. There is a recoil force, but the change in recoil force as a function of time is a big factor. Then there is the torque of recoil against your wrist or shoulder that causes the muzzle to rise, due to an imbalance in the axis of the bore and the center of rotation of the firearm which is a function of the grip or stock, center of mass, and center of reciprocating mass.

The AR was designed, quite ingeniously, to but the bore axis, center of reciprocating mass and stock all in the same line. Glock has favored lower bore axes compared to Sig and others to achieve similar results.

So while rounds have different recoil energy/force, how the shooter experiences them and how they react to them is somewhat subjective. And, it would tack a lot of dynamic analysis to explain the differences completely.

The worst perceived recoil I ever felt in a 9 mm semi-auto handgun was the HK P7. As Bruce Gray described it exactly: it feels like you’re holding a rebar in your hand and a huge guy is hitting the end with a sledgehammer.
But it sure has a low bore axis.

Thanks all for the information, links, and thoughtful input. I have my answer (and more) so I’m going to have this thread locked.

Again, you guys know some sh**!

quote:

Originally posted by sjtill:
The worst perceived recoil I ever felt in a 9 mm semi-auto handgun was the HK P7. As Bruce Gray described it exactly: it feels like you’re holding a rebar in your hand and a huge guy is hitting the end with a sledgehammer.
But it sure has a low bore axis.

Perceived recoil also involves the individual perceiving. I never thought much about recoil on a P7M8 (never shot a regular P7) and my son wasn’t bothered by it, but my wife thought it was horrible.

Low bore axis on the P7 yes, it does tend to increase recoil as the muzzle does not rise as much but the delayed breech unlock is more likely to be the culprit that really increases felt recoil. That gun is whole different breed of cat.

quote:

Originally posted by craigcpa:

quote:

Originally posted by jhe888:
There is a formula for free recoil. But that doesn't capture feel, which affected by stock shape, recoil pad material, etc. There isn't a simple answer.

After hrcjon (thanks) posted the formula, I knew mechanically it could be computed, but you quite succinctly pointed out variables I do not think can be quantified, hence, the formulas are moot?

Free recoil gives you a baseline number, but as you say, perceived recoil is what you feel, and it more subjective.