Walt Sherrill
Member
pblanc said:The reason is that upon ignition, there is an immediate retrograde force applied to the breech block that initiates muzzle rise during recoil. Even a tiny angular difference in muzzle rise will result in a significant shift in POI.
That's true with a revolver or a fixed-barrel semi-auto (like most .22s, .25s, .32s, and .380s). With these guns recoil begins to be transferred to the frame as soon as the bullet starts to move down the barrel. As the bullet moves on down the barrel, the barrel and frame move to the rear, and the force of rearward movement is transferred to the shooter's hand and the frame rocks back. And because the bulk of the force being transferred is above the hand causes the gun above the hand to move rearward and the barrel to rise. The barrel tilts because the grip frame is held by the hand.
What you describe is true of fixed barrel guns, but things work differently with most center-fire semi-autos, which generally use a variant of the Browning Short Recoil Locked Breech (SRLB) design.
With the SRLB design, the slide and barrel are locked together and move to the rear as soon as the bullet begins to move down the barrel. But the transfer of recoil force to the frame is briefly attenuated or delayed and as the slide moves horizontally to the rear. During the first part of that brief period of slide/barrel rearward movement, the bullet will exit the barrel before the barrel and slide has moved less than 1/10th of an inch to the rear.
The only rearward movement that can cause barrel rise which would affect the bullet's point of impact through recoil force transfer occurs during that 1/10th of an inch of slide/barrel travel. There's not much force transferred to the frame (via the recoil spring assembly) during that slight bit of slide/barrel movement. It can affect the bullet's point of impact, but not ANYTHING like what you describe in your comment above.
Once the bullet is gone, the rest of the recoil force -- which is MOST OF IT -- causes the barrel and slide to continue their rearward movement, and recoil force is passed to the gun's frame through the base of the recoil assembly and the barrel and moved shifted to the rear by the slide moving to the rear add to the effects of recoil. But none of this substantial recoil force has any effect on the bullet -- as it's already long gone.
Check out any number of the ultra-high-speed videos of SRLB semi-autos being fired on YouTube. You'll see that there is virtually no visible or measurable barrel rise prior to the bullet's exit from a SRLB gun's barrel. If the video continues, you'll see a lot of barrel rise and frame movement after the bullet is gone. You'll see something different with revolvers and fixed barrel semi-autos.