So how is it possible for a light load that leaves the barrel to not cycle the action while one too weak to exit does cycle?
I'll try to do this one more time. After a lot of head-scratchin' it's the only plausible explanation I can come up with. Like I said, I was skeptical my ownself...until I saw it happen. At that point, I was determined to figure out how it coould happen, and I gave it a lot of thought.
The 1911 is a short recoil operated pistol. The slide is driven backward, grabs the barrel by the lugs, and hauls it backward with it. At 1/10th inch of travel, the barrel starts to disengage from the slide. The bullet is gone and no longer exerting a forward drag on the barrel and resistance to the slide. (Here is the "delay" in the delayed blowback, incidentally.) At .200 inch...the lugs are clear. At .250-inch, the barrel is completely on the frame bed and the slide soldiers on by means of momentum conserved during that first 1/10th inch...while the bullet and slide were being accelerated by force.
Without the bullet's influence, it doesn't take all that much force to move the slide fast enough to give it the momentum that it needs...and it doesn't take all that much momentum to keep it moving after the bullet exits. You can hand-cycle it as fast as it moves when it's fired...or even faster.
If enough force was generated to drive the bullet halfway through the barrel, there was more than enough to drive the slide.
Go drop 7 grains of Bullseye into a case and top it off with a tuft of cotton...and fire it in a pistol to demonstrate just how little force is needed. I was able to drive one far enough to get the hammer to half-cock with 5 grains...and the gun had a 16-pound recoil spring and a 23-pound mainspring in it.
All the bullet has to do is keep moving long enough to keep the slide moving until the barrel drops. Once that happens, the bullet's location is irrelevant. It can be in the barrel or 20 miles downrange. Its influence on the system...its delay...is over.
Oh and how is a 1911 delayed blowback?
If you think about it, there's really very little difference between the straight blowback and the recoil operated. Both slides are "blown back" and both move because of recoil.
Recoil is nothing more than acceleration backward in response to a force applied between two objects. Force drives the bullet forward away from the breechblock...and it drives the breechblock backward away from the bullet. So...the "blowback" is recoil operated, too.
The main difference is in how the opening of the breech is delayed until pressures fall to safe levels. In the short recoil design, the barrel is tied to the slide for a short distance, with the mass of the slide and barrel...the springs...and the bullet's drag working together to impose the delay.
In the blowback, the slide moves independently of the barrel, and only its mass and the action spring keep the breech from opening too soon. That's why blowback pistols have such heavy springs or massive slides...and why recoil operated pistols have relatively light springs and slides. In the blowback, the spring has a dual purpose. To help delay the slide and to return it to battery. In the short recoil pistol, the spring's only real purpose is returning the slide to battery.
