After a discussion/Disagreement on another thread in regard to early unlock timing and the phenomenon of gas and powder blowback through the breech...I thought I'd take a little time to address it in the interest of understanding this marvelous Browning Brainchild.
First...Understand that the barrel can't unlock while the bullet is present and the barrel and chamber is pressurized.
Ain't gonna happen...and if the timing is so early that the link tries to disengage the barrel from the slide, the link will
stretch and probably fail in very short order. (The exception would be that the link stretches to the point of delaying linkdown until the bullet has left. Most of the time, this causes problems with delaying linkdown and drop timing too much, with resulting damage to locking lugs...but that's meat for another clinic.) A little study on how the 1911 achieves its locked breech...when it locks...and when and how it unlocks will make it clear. The breech locks when the gun fires, and unlocks when the pressures have dropped. The link doesn't "unlock" anything. It only draws the barrel down and out of the slide AFTER unlock has occurred.
Read that again and think about it. The "Locked Breech" 1911 is not locked until it fires. The term "Locks up like a vault" and, Locks tightly into battery" are technically incorrect, and misleading. If the barrel is closely hand-fitted, it's wedged into battery via an interference fit in the related parts...but it is NOT locked.
So...How does the gas blowback happen?
This condition is rare. So rare, that I've only seen it happen with a half-dozen or so pistols in over 40 years. It requires that the timing be just perfect, with a very narrow window of opportunity in order to happen. A thousandth of an inch or two greater center-to-center distance in the link, and it won't happen. The mechanics of the event are simple, if we remember that any force that occurs in nature tends to follow the path of least resistance.
The start of the linkdown phase begins at roughly .100 inch of slide and barrel travel. This will vary for several reasons, but is generally controlled by a combination of varying dimensions within the gun. Also known as "Tolerance Stacking."
No need to go into great detail other than to say that the slide's installed height relative to the slidestop's crosspin hole
and the link's distance from hole center to center are the main factors. Lower lug geometry also plays a role, but a smaller one. If the linkdown begins at say...about .090 inch of slide/barrel travel, you 're very close to seeing gas blowback. In these, you will probably notice that you can remove the extractor from the slide, and the gun will continue
to extract and eject, albeit erratically. The reason being that residual gas pressure within the barrel that hasn't had time to escape. Note that missing extractor function can occur without apparent gas blowback, but if the gun will function without the extractor, there has to be some amount of blowback. It's just not enough to notice. In fact, there's a amall amount of blowback even in a perfectly timed gun. That's where all the carbon and other crud in the ejection port and on the breechface come from. It happens after the bullet has left, and the case has sprung back...and blows past the walls of the case and into the breech.
This residual gas pressure occurs just at the instant of, or just after the bullet breaks into the air. In some, it may occur
when the base of the bullet is in the muzzle crown, where the rifling is cut on a taper...and technically hasn't actually cleared the barrel completely. The gasses impinge on the bullet base, and are forced to blow out sideways though a narrow gap...such as the barrel to cylinder gap on a revolver. This gap only lasts a fraction of a nanosecond...and here lies the narrow window for blowback through the breech.
Pressures are low enough to end the "locked breech" part of the function, but a small volume of gas and pressure is still present. The slide is moving, and the link is drawing the barrel downward...and the breech is open...though not by very much,Primary extraction has begun. The case walls have sprung back... the walls have broken free of the chamber, and the residual gasses have found a path of lesser resistance than escaping sideways past the bullet base and muzzle crown...and they "follow" the empty case as the extractor pulls it clear. Here's they've hit another set of paths of greater and lesser resistance, since the case can't contain the volume of gas, and they again follow the path of least resistance, and escape into the now open breech area. It would appear that they're blowing straight back, but in reality are blowing in all directions. Up...down...sideways...diagonally...forward, and backward...the same as any force vector.
The fix for this situation is often as simple as a slightly longer link...maximum of .003 inch... or elongating the bottom of the link's hole to delay the start of linkdown by a couple of thousandths of an inch...again, for a maximum of .003 inch.
Here endeth the lesson.
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