After some feedback from JohnKSa, I finally went "duh!". I see now where Polyphemus and I are talking past one another. He didn't want to know what I thought he meant by the source of the force. He wanted to know how recoil force is coupled to the frame during the time the bullet is in the barrel. Some days I am slow on the uptake.
Obviously, when firing a semi-auto pistol, some part of the momentum splits off to the slide during barrel time or the gun wouldn't cycle. The portion that gets to the frame while the bullet is still in the barrel is less obvious as to its mechanism. We know it is real because, as the OP reports, his heavier bullets impact 2" higher, plus the video clearly shows it. It is less than in an equivalent single-shot or revolver gets because they share nothing with a slide, though equivalence is hard to establish exactly as you need the same moment of inertia for the vertical plane rotation and the same breech-to-muzzle length. In that instance, the pistol will have less muzzle rise because of sharing momentum with the slide which does not add to the frame momentum until the end of its travel.
In the semi-automatic pistol, some of the coupling is from friction, some from the preload on the recoil spring, some from the linkage to the frame as long as the barrel and slide are still locked, and some from the effort required to cock the gun. The last one is responsible for the lion's share of it.
Browning's original 1911 design required excessive cocking effort. The firing pin stop had a square bottom. This put the cocking force into a point far down the hammer and closer to the hammer pivot pin, so it had a short lever arm, aka, less mechanical advantage than most folks have now. This is because most use the later 1911 A1 firing pin stop, which has a large radius on the bottom, raising the point of contact with the hammer and making it easier to rack the slide when the hammer is down. The is change was made by the military because of soldier's complaints about racking effort on the original.
When EGW came out with their flat-bottom firing pin stops a number of years back, I got one for the full-size 1911 I took to Gunsite originally. Racking the slide with the hammer down does take more effort. However, a friend I was shooting with commented that my muzzle was hardly rising at all (fast recovery). This is because the percent of momentum going to the slide was significantly reduced, so it didn't yank the gun up and around nearly as much when the slide hit the frame through the recoil spring guide. Apparent recoil was significantly reduced; much more than a shock buffer accomplishes. And, you guessed it, with more momentum passing to the frame, my front sight was now too short. At 50' I was about 2 inches higher than I had been with hardball, making the front sight about 0.023" short.
Obviously, when firing a semi-auto pistol, some part of the momentum splits off to the slide during barrel time or the gun wouldn't cycle. The portion that gets to the frame while the bullet is still in the barrel is less obvious as to its mechanism. We know it is real because, as the OP reports, his heavier bullets impact 2" higher, plus the video clearly shows it. It is less than in an equivalent single-shot or revolver gets because they share nothing with a slide, though equivalence is hard to establish exactly as you need the same moment of inertia for the vertical plane rotation and the same breech-to-muzzle length. In that instance, the pistol will have less muzzle rise because of sharing momentum with the slide which does not add to the frame momentum until the end of its travel.
In the semi-automatic pistol, some of the coupling is from friction, some from the preload on the recoil spring, some from the linkage to the frame as long as the barrel and slide are still locked, and some from the effort required to cock the gun. The last one is responsible for the lion's share of it.
Browning's original 1911 design required excessive cocking effort. The firing pin stop had a square bottom. This put the cocking force into a point far down the hammer and closer to the hammer pivot pin, so it had a short lever arm, aka, less mechanical advantage than most folks have now. This is because most use the later 1911 A1 firing pin stop, which has a large radius on the bottom, raising the point of contact with the hammer and making it easier to rack the slide when the hammer is down. The is change was made by the military because of soldier's complaints about racking effort on the original.
When EGW came out with their flat-bottom firing pin stops a number of years back, I got one for the full-size 1911 I took to Gunsite originally. Racking the slide with the hammer down does take more effort. However, a friend I was shooting with commented that my muzzle was hardly rising at all (fast recovery). This is because the percent of momentum going to the slide was significantly reduced, so it didn't yank the gun up and around nearly as much when the slide hit the frame through the recoil spring guide. Apparent recoil was significantly reduced; much more than a shock buffer accomplishes. And, you guessed it, with more momentum passing to the frame, my front sight was now too short. At 50' I was about 2 inches higher than I had been with hardball, making the front sight about 0.023" short.
