In response to one of three questions:
Without going into small details on vectors of force...the best way to understand the recoil cycle is to first study the locked breech system itself.
A few things to keep in mind are:
The barrel isn't supposed to lock on the link...at least not in a properly fitted gun that is in-spec. The link's sole function is to unlock the barrel.
The recoil spring has very little to do with unlock timing. It has almost no influence on the slide's initial movement, and it has nothing to do with
containing chamber pressures. The mainspring has more influence on
delaying the slide's initial movement, and is a function of the slide's
mechanical leverage in recocking the hammer. Remember the point of
the slide's "Initial Movement." It will have more meaning soon.
The barrel and slide are locked together by a series of lugs and slots
that mesh in the horizontal plane. Vertical lockup is achieved by the
lower barrel lug camming upward on the slidestop pin, and is a topic for another discussion. Static on the bench, the breech isn't locked. "Lock" begins when the vector of force is applied and bullet movement begins.
Prior to that, the only horizontal "lock" is provided by the recoil spring's
tension.
As the bullet is forced through the bore, the barrel is pulled forward. At the
same instant, the slide is hammered backward in the equal and opposite reaction that we've studied as one of Newton's laws of motion. This
vector of force is applied equally in all directions, and the barrel and slide are in a condition of isometric lock...but this ends in a nanosecond
as soon as the bullet begins to move.
The vector of force gradually becomes unbalanced with bullet movement,
and the faster the bullet moves, the more unbalanced it becomes.. and the force follows the path of least resistance...The slide. The slide, due to its greater mass, moves slower than the bullet, and because of that mass, pulls the barrel...bullet and all...rearward with it.
Slide and barrel move in a straight line together for approximately 1/10th of an inch. The link pivots on the slidestop pin and upon reaching a point in its arc determined by its length between hole centers, starts to change
the barrel's linenear movement and forces it to start changing direction to downward. The unlocking phase begins at that point. The point can be physically seen by looking at the lower lug's shape at the front...where it forms a radius that allows the barrel lug to fall off the slidestop pin. The barrel's downward movement continues until the slide has moved one-quarter inch, and the barrel is linked down completely and on the frame bed. Complete unlocking occurs at some point before this quarter-inch point is reached, but that's the point that the barrel must be
in the frame bed so that the slide can continue to move without contacting the barrel's locking lugs, assuming that the barrel's impact surface in the frame is correct in relation to the rear of the lower lug.
The recoil cycle is completed by the momentum imposed on it during that first 1/10th inch of movement. By the time that the unlocking phase begins, the bullet is gone, and the "Equal and Opposite" reaction to
the bullet is gone with it...and Conservation of Momentum has taken over
to complete the cycle.
This is a point of contention in Jerry Kuhnhausen's theory of "Balanced Thurst Vector" in which he states that the slide begins to move AFTER the bullet exits, when the balanced thrust vector that pulls the barrel and slide in opposite directions is broken by bullet exit. This...simply put...can't be. If the bullet exits the muzzle BEFORE the slide moves...the slide won't move. The slide has to move while the bullet is still in the barrel. As noted, this distance is very short...but it has to move before the bullet exits because without the bullet to act as a means to redirect the vector of force against the slide, the slide will stand still...or at best...move very little as a result of any remaining expanding gasses remaining in the bore after the bullet exits.
After barrel linkdown, it's a simple matter of the slide obeying another of Newton's laws, and remaining in motion until forced to stop by an outside influence....the impact surface in the frame. The recoil spring has compressed, and it's stored energy forces the slide to return to battery.
Next: A recoil spring study.
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