Let's clear the air.
Before I start, let me give you full disclosure. I am a mechanical engineer and work at a major automotive manufacturer (Honda). This means I have a firm grasp on physics. I also shoot. A lot. I also handload and have shot the 9mm. A lot. I've also worked on handguns and played with adding weight, recoil (action) spring rates, mainspring rates, and other physical changes that are beyond the scope of this conversation.
No, I'm not trying to beat my chest, I'm just telling you that I do have some experience with this and many of you are confused to some degree.
As you know, the 9x19mm Luger cartridge comes with three common bullet weights: 115gr, 124gr, and 147gr. There is not much of a difference between each step, but the 147gr bullet is considered "heavy-for-caliber." There is a considerable increase in mass (27%) when you jump from the 115gr to the 147gr bullet.
When you push the two bullets at the same velocity, there is a considerable difference in perceived recoil, momentum, and muzzle energy. That is easy enough to see. Push the 147gr bullet at 1000 fps and you'll have 326 ft-lbf of energy at the muzzle. Push a 115gr bullet at the same velocity and you have 255 ft-lbf of energy at the muzzle. However, ammunition manufacturers rarely load the 115gr that slow or the 147gr that fast. You typically see advertised velocities of 1150fps for the 115gr (337 ft-lbf) and 950fps for the 147gr (294 ft-lbf). These numbers vary greatly depending on the manufacturer and intended purpose of the cartridge.
In the competitive shooting world of IDPA, USPSA, and 3-Gun, you have a term called POWER FACTOR. PF is essentially the shooter's word for "momentum" or "impulse." We calculate PF by simply multiplying the muzzle velocity (ft/s) by the bullet weight (grains) and divide by 1000 to arrive at the PF for that load. "Minor" power factor is 125 and "major" power factor is 165.
You can see that in order to make minor PF in 9mm, you must make a different velocity for each bullet mass. The 147gr must make ~850 fps (235 ft-lbf). The 124gr must make ~1008 fps (279 ft-lbf). The 115gr must make ~1087 fps (302 ft-lbf). As you can see, each one of these loads makes the same amount of impulse, but the lighter-mass bullets produce much more muzzle energy than the heavier bullets do.
The increase in kinetic energy results in a greater acceleration of the bullet, increasing the amount of force that accelerates the slide (increased bolt velocity), which results in a "snappier" recoil. If you ever get to compare a .45 ACP making "minor" power factor with a 230 gr bullet at 544 fps, you'll quickly see why the 147gr bullet has less perceived recoil than a 115gr bullet! This is also why the .40 S&W cartridge is oft-quoted as having a more violent recoil than the .45 ACP, because you have a lighter bullet (180 gr) running at a much higher velocity (1000 fps) that makes much more energy (400 ft-lbf) than the typical .45 ACP load (230gr bullet at 835 fps = 356 ft-lbf)!
All of this, of course, hinges on the same variables held for each caliber including primer brisance, powder burn rate, and chamber pressure. The powder mass typically decreases with the bullet mass used, so instead of 5.1gr of powder behind a 124gr bullet, I'd use maybe 4.0gr behind the 147gr pill.
I hope this sheds light on why people say a 9mm with 147gr bullets has less perceived recoil than the same pistol shooting 115gr bullets.
I'm glad it's healed now 
