Here is an X-Ray photo of a 1911 firing, with the bullet just short of the muzzle. You can see the bones of the shooter's hand if you look closely.
The slide has moved rearward about 1/10th inch. It clearly shows the barrel lugs' front faces bearing on the rear faces of the slide's as the slide pulls the barrel rearward... against the bullet's forward drag... which is holding the barrel forward under friction.
This is how the 1911's locked breech works. It locks horizontally... under pressure... while the bullet is present and moving. Once the bullet is gone, the breech is unlocked.
This is the best picture I've seen yet. It illustrates perfectly how this
thing works... and all it takes is a little visualization to see and
understand how and why the bullet acts to delay the slide. It has to. The only
way that it wouldn't is for the bullet to move forward... stop and wait for
the slide to pull the barrel to the linkdown point...and then start moving
again. Ain't gonna happ'n Cap'n. While the bullet is moving, it drags forward
on the barrel while the slide is pulling the barrel backward.
Excellent photo!
Wherever did you come up with this? I notice it's numbered #20. Are there more x-ray pictures, showing the firing sequence?
Now that I have a visual of what I have seen discussed - at length - around here, at what point does the hammer begin to move ie re-cock? I think I have read that it happens prior to the slide moving rearward.
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Are there more x-ray pictures, showing the firing sequence?
Don't know. I swiped this one from a post on THR.
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at what point does the hammer begin to move ie re-cock? I think I have
read that it happens prior to the slide moving rearward.
The hammer starts to move the instant that the slide starts to move, assuming that the strut isn't so short or the mainspring cap isn't mislocated and preventing the hammer from remaining in full, spring loaded contact with the firing pin stop.
The hammer is forward under something like 18 pounds of pressure from the 23- pound mainspring. It can't move toward cock until something forces it...and that would be the slide.
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Also take notice that the muzzle hasn't started to flip... at least not
enough to notice. Why?
Because the recoil spring hasn't compressed enough to apply a large degree of forward/backward force to cause the frame to recoil yet...and it won't until the spring is at roughly halfway to full compression.
I think the muzzle has flipped some, maybe not a large amount yet. There is a recoil force directed backwards caused by the case pushing against the breech face, and that occurs EXACTLY at ignition. I have seen "g" force plots for auto and revolver guns: the autos show a medium height impulse at firing, a gradually increasing (lower) ramp up as the recoil spring compresses, then another medium pulse when the slide hits the frame. I think the initial firing pulse recoil does cause some muzzle flip before the bullet leaves, since I have checked bore alignment versus sight alignment with a laser and the bore is ALWAYS aimed lower than the sights. On my 9's, it's maybe 2" under line of sight at 15 yards. That means the "muzzle flip" rise due to rotation from recoil does bring it up a bit.
Interesting point is that revolver "g" plots simply show a big pulse at firing, no other forces. For comparable .38 (125 grain) ammo flying at about 1000 fps like the 9's, the bore axis is about 4" lower than line of sight. This shows a wheelgun which has all the recoil impulse at discharge gets more muzzle rotation before the bullet leaves the barrel. The slide assembly on an auto does reduce peak recoil impulse some and therefore, reduces muzzle rise before bullet exits the barrel.
Of course, the amount of muzzle flip to get the POI up a few inches at 15 yards is only in the ballpark of maybe .030 - .040", so you wouldn't see it from a side view photo.
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There is a recoil force directed backwards caused by the case pushing
against the breech face, and that occurs EXACTLY at ignition
Precisely... assuming zero headspace. The time required to drive the case back against the breechface a few thousandths would be all but immeasureable... so we'll agree that it's at the same instant for all practical purposes.
The thing about an autopistol is that, the slide and barrel assembly is the gun, while the frame is essentially the gun mount... and it's mounted on a rail with no mechanical connection other than friction and the action/recoil spring to transfer the gun's movement to the frame.
The revolvers have a fixed breech, so they start to flip at the instant of recoil impulse. Not so with an autopistol... whether locked breech or blowback.
Imagine for a minute, a frame with 30-foot rails and the slide mounted way out on the end. The barrel links down at the normal distance of slide travel, and there is no spring between the slide and frame. Let's also imagine that the slide/frame rail movement is unbelieveably butter-smooth, with only the barest hint of friction as they slide across each other.
You could fire the gun and feel nothing in the way of actual "kick" when the recoil forces drove the slide backward... and because it would be so nearly out of steam by the time it hit the impact abutment... about all you'd get is a slight nudge.
When the slide compresses the spring, the spring's resistance works equally against the slide and frame, becoming a vectored force in a separate closed system. The farther the spring compresses, the harder it pushes against both...and the more "recoil" you feel. At the highest point of spring load, the slide hits the frame's impact abutment... and the muzzle flips.
Remember that springs work in both directions, like any other force vector. Whatever force that it imposes on the slide, it also imposes on the frame... in the opposite direction.
Because the slide only compresses the spring about a 1/10th to 1/4th inch at the point of bullet exit... all you feel from the spring is the amount of force generated by the preload and the extra bit of compression.
You can see how this works by watching Virgil Tripp's excellent slow and stop-action video, which is here... somewhere. A sequence with the gun spring tethered to a bench and another behind it, firing again... untethered. There is no movement with the tether attached, and very little without it until the slide is well past the halfway point, but before frame impact.
Anybody else noticed that the pistol shown is a pre-11A1?
That X-Ray may be older than we think...
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Because the slide only compresses the spring about a 1/10th to 1/4th inch
at the point of bullet exit... all you feel from the spring is the amount of
force generated by the preload and the extra bit of compression.
Actually, Master Tuner, Sir, you don't feel anything from the preload, because the preload is already in static equilibrium between the slide and the receiver. The energy to achieve the preload was exerted when some doofus pushed down/in on the recoil spring plug and locked it in place with the barrel bushing. The action of firing the round and the slide starting to move doesn't create or affect the preload. The only vector force active is the additional force imposed on the spring in the course of moving the slide that 1/10th of an inch or so. If the spring's rate is on the order of 1 pound per inch of travel/compression (I know I did the research on this, but I'm too tired to look up the exact numbers), then the force involved in that 1/10th of an inch is about 1/10th of a pound.
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Actually, Master Tuner, Sir, you don't feel anything from the preload
Until the slide moves. The slide has to overcome about 9 pounds of resistance before it can move... and you get 9 pounds of push against the frame.
The preload is static up until the trigger is pulled then as the the barrel is pulled back by the slide and the feet come off the pin the preload is passed off to you. Grip the pistol and push hard enough on the slide to move it back .100". A 5" 1911 with a 16# recoil spring will preload about 8# in battery, moving the slide back .100" will add about 4oz. and since the lower feet are no longer holding the load you feel the 8# and the 4 oz.
Well Johnny, it's been written about, illustrated, filmed in slow-motion, and now x-rayed. Do you think this will finally settle it.
The mechanical connect between slide and frame at the initial ignition impulse is the hammer and it's spring. The slide has to exert considerable force to get the hammer to deflect against that spring so the slide can get out of battery, also there is inertia of the slide assemby's mass.
I agree the moving slide assembly does act to spread the recoil out in time. They use the same principle on battleships where the whole gun is allowed to slide backwards when it fires which spreads the recoil over a wider pulse which reduces it's peak amplitude.
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The mechanical connect between slide and frame at the initial ignition
impulse is the hammer and it's spring.
Yep. Forgot to mention that one, Log. I got wrapped up in the other stuff. The point was that there's very little actual recoil impulse felt through the frame on ignition. If the shooter has a firm grip, you'd have to look close to see any movement at all... and you'd have to look at it in a slow-action sequence.
As for the add-on: "When does the slide move" part... that's already been established.
I wanted to show the barrel and slide lug relationship... and how the lugs are bearing against one another as the gun cycles. There are many who don't understand and can't accept that the slide pulls the barrel backward and that the bullet is resisting that function via its frictional forward drag on the barrel. Hence... the bullet IS part of the slide delay. Not so in a straight blowback because the barrel isn't connected to the slide.
Also note that the resistance provided by the bullet is present in a fixed- breech weapon... like a bolt-action rifle. (Somethin' tells me that I'm gonna wish I hadn't said that...)
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If the shooter has a firm grip, you'd have to look close to see any
movement at all...band you'd have to look at it in a slow-action sequence.
Yep, with a strong grip it's probably tiny like I estimated maybe .030" rise at the barrel end based on what I see as the difference in bore axis alignment and sight alignment on my guns to get POI to coincide with POA.
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What would be interesting, is, if a grid was in the background and one
horizontal line was parallel to the bore... Along with a milli-second
timer...
Not needed to estimate the distance of slide travel, Pappy. If you'll look at the gap between the slidestop pin and the lower lug feet, you'll notice that it's a bit less than half the diameter of the pin... which is .195-.199 inch +/- a half-thou. The bullet still hasn't left the muzzle, so the slide still has a few more thousandths to go before the barrel reaches the linkdown position. I'll go ahead and estimate the distance of slide travel in the photo at .075-.085 inch... just short of the barrel reaching the beginning of the linkdown phase.
You'll also notice that the barrel hasn't yet started to link down, as it's still in full vertical engagement as seen by the fact that the slide's lugs are still in contact with the top radius of the barrel's lug slots.
Indeed... if it were being linked down at this point... while the lugs are being forced against one another opposite directions... the lugs would be damaged and the link would be stretched. Although the pressure-induced lock at this point is far lower than it is at peak pressure... maybe 10-15% of peak...that's still a lot of horizontal shearing force to overcome in order to pull the lugs apart vertically if the barrel did actually link down enough to disengage. It's a lot of stress on the link that the link wasn't designed to bear, and the frictional resistance to a vertical move at this point would round off the corners of the barrel and slide lugs in short order...raising heavy flanges and eventually causing the drop clearance to disappear... which would then bring on more lug damage from impact when the barrel stops against the vertical impact surface.
The time can be calculated by factoring in the distance of bullet travel, taking into account that the barrel is being yanked backward off the bullet by a 10th inch at exit, effectively shortening the time required to reach the muzzle by the time that it takes the barrel to move a 10th inch backward. And... before it starts... I won't get into a drawn-out argument on that last point. It'll either be seen and understood, or it won't... but that is the reality. It ties in to the bullet-induced delay of the slide... and I've argued that one until I refuse to do it any more. As with the other point... you either see it or you don't.
Because the pistol in the photograph is an old one, I'm guessing that the photograph itself is also very old, and likely was made at a government arsenal during the early days... just to demonstrate how and why the gun works... and probably because somebody else in those days didn't believe/couldn't accept that the slide moves before the bullet leaves, and wouldn't accept that Newton 3 dictates that it must work that way because equal means equal in every way... including the onset of the reaction side of the action/reaction event.
A recap:
Assuming zero headspace, the slide starts to move at the same instant that the bullet starts. The bullet exerts a forward drag on the barrel while the slide is exerting a rearward drag on it. The bullet's forward drag resists the slide in pulling the barrel rearward. The lugs lock horizontally under pressure in opposing directions... under a shearing force. This is the locked part of locked breech. Before the gun fires, there is no "lockup" and there is no locked breech. The breech is simply closed and held under spring tension... but it isn't locked. Don't take my word for it, though. It's clearly described in the original patents... in the words of John Browning and translated into legalese by the patent attorneys who wrote it up.
Finally, there are only minor differences between the short recoil operated pistol and the straight blowback. They work pretty much the same way, and the only real difference is that the slide of the blowback operates independently of the barrel. The locked breech/recoil operated pistol is almost a delayed blowback. Only the fact that the barrel remains tied to the slide, and moves with it for a short time and distance prevents it from being so.
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If someone builds a .45 ACP or equally powerful pistol, what sort of
problems would they encounter?
It's been done. The Hi-Points are straight blowback in operation. The problems lies in delaying the breech opening until the bullet has exited and pressures have dropped low enough to safely allow it to open. The old open- bolt Ingram MAC-10s were also straight blowbacks.
Blowback and locked breech differ mainly in the method used to accomplish that delay. Blowbacks use slide mass and/or recoil spring tension. Locked/recoil operated pistols use lugs... a mechanical connection instead of an inertial/spring-loaded method... to keep the barrel and slide from separating until the bullet has exited. The locked-breech pistol, such as the 1911 and others of similar design utilize the mass of the barrel briefly to add to the slide's total reciprocating mass, increasing the inertia-induced resistance. Think of it like a variable spring... except it's a variable mass at work. Then, there's the effect of the bullet dragging the barrel in an opposing direction that also adds to the slide's delay.
If the 1911 were to be converted to straight blowback function without increasing the slide's mass enough to compensate for the barrel and the bullet's effects... the recoil spring would probably have to be in the neighborhood of 35-40 pounds in order to avoid problems.
The Browning short recoil system is almost... ALMOST... a delayed blowback. The only minor detail that keeps it from being so is the fact that the barrel is temporarily attached to the slide... and moves backward with it... instead of being fixed to the frame.
Little more than a technicality, and in truth, it probably should have been described as a delayed blowback.
The delayed blowback... the straight blowback... and the recoil operated pistols are ALL recoil operated. That is, they function because of an action/reaction event that occurs between the bullet and the breechblock via the vectored force provided by the burning, expanding gas. Force forward... Force backward. That simple.
This thread explains something that always puzzled me, and hasn't been mentioned explicitly here so far: When I changed to a lighter mainspring, my gun started shooting high!
I always thought this was crazy and figured I must have just not noticed it before because it was a new gun to me or whatever. But now it makes sense (I think).
bountyhunter mentioned that the muzzle lifts a tiny bit from the initial recoil impulse. This lift would be a little bit higher if there is less resistance, as there would be with a lighter mainspring. This would of course cause the gun to shoot higher!
I suppose a square firing pin stop would also reduce the initial recoil impulse/lift. I'm off to read the sticky on that now.