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.
New here. Friend asked me to stop by. Doing some high speed pics maybe this weekend if things fall right will have some high speed photos of bullet at the end of barrel, half way out and all the way out. With markers on slide to show movement of slide to frame.
Hey Steve! Welcome aboard. The pictures would be great!
On the one you've posted... unless the light and shadows are playin' tricks... looking at the muzzle, rear of the slide to frame position, and the barrel in the port... It appears that the slide has moved almost to the point of complete barrel linkdown with the bullet about 4 inches out. Assuming a muzzle velocity of 800 fps, that would make the slide's movement there occur in roughly 1/2400th of a second. Figuring that the bullet has moved a total of about 8-9 inches to reach the spot shown... and plugging in estimated average bullet velocity on its trip from chamber to muzzle... it would seem to me that the unlock/linkdown phase started at just about the point that the bullet broke free of the barrel... or maybe an inch out. Since the slide and barrel move together for roughly .100 inch when unlocking begins, the time frame would appear to be about right for that to occur, since it appears that the slide has moved twice times the distance needed... about .200 inch or so.
Lookin' forward to the stop-action photos.
Well, got everything gathered for the photos except the "trigger" to set off the flash. I need a switch that mounts up against the end of the barrel. It will have to be a "one time use" switch, since the bullet will destroy it. So I will have to make 20 or 30 of them. And locate them at different distances from the barrel. Even put one about a half inch in the barrel. So it will probably be about the size of a couple needles, as not to obstruct the bullet coming out!
I got an 35mm camera and a very short duration flash from work. The only reason I got that was they never use it anymore. Plus I will have to mount this assembly in a dark box, since the picture will be a sort of time exposer, with the flash making the picture.
John,you right I work for JPL in Pasadena, but I am not one of the guys in the white coveralls. I work in the transportation dept as a truck driver. And my hobby is 4X4 Jeeps, but starting to like the Colt 45 auto.
I do not know, I do not like the idea of putting things inside the barrel, something bothers me with this idea.
Triggering the strobe on sound is what is used most of the time. If you place the pickup on the gun near the hammer you can get 'bullet in barrel' pictures from the hammer impact. Placing it futher away allows for bullet out of barrel. We place the pickup about 45 degrees to the side from boreline.
Well, I talked to a couple guys at work. One of them said that using a flash in a dark box would work, but the muzzle blast would wash out the picture of the bullet. Which in this picture they were right.
Here is a Colt Government model pistol showing the initial slide movement. Switch wire is taped to slide and wrapped across muzzle. The 230 grain round nose jacketed bullet can just be made out in the glare of the muzzle flash; it's left hand rifling marks visible. There is a one inch paper sticker on the slide and frame which shows that the slide has recoiled about 0.16 inches while the bullet was still inside.
The slide and it's attached parts weigh 17.5 ounces; or 7660 grains, and the bullet travels 4.4 inches. 4.4 x 230 / 7660 = 0.13 inches. The reaction of the gunpowder accounts for the rest. Recoil spring tention and bullet velocity are irrelevant.
Aha!
Which pretty much blows Kuhnhausen's theory to Helen Gone.
He states that there is no slide movement until the bullet leaves the muzzle and breaks the balanced thrust vector.
In this photograph, showing about .130 inch of slide movement at the instant the bullet breaks muzzle contact... which puts the beginning of unlock timing just a bit late. Ordnance spec pistols begin the unlock phase at .090-.110 inch of barrel movement rearward, while match-tuned guns can delay it until .125 or a little more to allow the case to be extracted while the barrel is at a less severe angle.
I'd be willing to bet that here is a pistol that will function pretty well with the extractor removed.
Good pictures Steve! Keep'em comin'.
So by the time the bullet exits the muzzle, the barrel is unlocked... with ya so far... but @ .13 isn't the barrel heading for its bed? In the midst of tilting? Or at least right at start of it anyway.
So is it physically possible for the barrel to be tilted (headed for bed) before the bullet exits the muzzle? Would using different links affect that? As link length affects the timing of barrel link down.
Would like to take the measurement of this here 1911 specimen used in the pics to see at what points does it actually start to unlock, is fully unlocked, and then is in bed (nighty night!)
Also while my fertile slide rule mind is running full steam here (the wheel is turnin', but the squirrel just ain't movin')... the barrel can't achive the point of linking down with the bullet still in the barrel, otherwise all your shots would go high due to the barrel tilt. But if the gun is short linked, that would bring the barrel down faster which means the bullet is closer to the mouth of the muzzle instead of farther away. From the pic I'd say that total link down of the barrel (without crunching numbers) is less than 2" from the muzzle?
Will be doing some measuring to see at what point my 1911's are in full link down... want to see how different they may be.
Tilt!
Wichaka said:
So by the time the bullet exits the muzzle, the barrel is unlocked... with
ya so far... but @ .13 isn't the barrel heading for its bed? In the midst of
tilting?... or at least right at start of it anyway.
Depends on where the unlock sequence begins. Some will start as early as .090 inch of travel... Some will start as late as .125 inch or more.
There's not a danger in starting it early as long as chamber pressure isn't at its peak... but the lower the better. Guns that delay the onset of unlock timiing to .110 or more will usually function without an extractor, and their extractors last forever, since they're loafing. Guns that start early won't function without an extractor, because the extraxctor has to pull the case free both at an angle and against low chamber pressure.
Quote:
So is it physically possible for the barrel to be tilted (headed for bed)
before the bullet exits the muzzle? Would using different links affect that?
As link length affects the timing of barrel link down.
Yes. Re-read the above. When I got copies of Kuhnhausen's shop manuals, he explained the effects of delaying unlock and linkdown timing in match-grade pistols. I'll find the page number where it's covered and post it later.
Quote:
Would like to take the measurement of this here 1911 specimen used in the
pics to see at what points does it actually start to unlock, is fully
unlocked, and then is in bed (nighty night!)
What I'd like to do is test another gun with the same ammunition lot. You'll likely see a much different result... and then send me the top end of the second gun so I can fit a firing pin stop with a .075 radius... and install a 23# mainspring... and repeat the test again to show how the linkdown timing is affected.
Another test with this same gun firing a round of Remington 185-grain +p will also show a different bullet/slide position.
Want to make life easy for your extractor? Delay the linkdown timing a bit.
Like I said... the gun pictured above will probably function without an extractor, since its timing already seems pretty late.
Fascinating stuff!
Getting ready to do some last minute Christmas shooping. Ran across this article. Long and detailed, so be ready to drink a few cups of coffee 1911Tuner!
link: yarchive
Interesting discussion, and pretty well spot on, I'd say.
The recoil cycle can be altered as to the timing of bullet exit in relation to the amount of slide travel by simply going to a lighter faster bullet... even though the momentum generated against the slide would be the same. Since the mass of the slide remains constant, as does its inertial resistance to acceleration, the bullet will still exit at an earlier point in the slide travel.
This leads to some conclusions. Since the recoil cycle is completed by the momentum that it gets from the bullet while it's in the barrel... getting the bullet out quicker would tend to decrease the amount of momentum available for the slide to absorb because it reduces the bullet's dwell time within the barrel. My theory is... and has always been... that whenever a lighter, faster bullet is used, the recoil spring load should be lowered in order to utilize the amount of momentum available for the cycle. This goes in direct opposition to the generally accepted wisdom of using a heavier spring for light, high- velocity ammunition of the +P category...and practice has bron this out whenever I ran into a pistol with functional issues with this type of ammunition. The owners had... almost without exception...upped the recoil spring load for their choice of ammo. This hasn't been as critical until bullet weight has gone below 200 grains and velocities above 900 fps, though. It's the 185-grain screamers and near-proof pressures that give rise to the problems in most cases.... and this is amplified whenever barrels shorter than 5-inches is part of the picture. Since the lightweight, high pressure screamers are often used in order to offset the velocity loss and help to insure expansion reliability... this is likely why we see so many pistols in the Commander length class and shorter produce so many functional problems.
Even though the earlier bullet exit and resulting loss of momentum would be offset by the lighter slides, it seems that there's a point of diminishing return... and since the shorter pistols are generally equipped with high spring rates... it soon becomes a self-perpetuating cycle.
Stiff springs are partly necessary with lightened slides... but not for frame protection. It's because the forward momentum of these short, light slides sometimes isn't enough for reliable feeding and return to battery. Lighten the spring enough to provide full travel in recoil, and you may lose too much momentum for the other half of the cycle.
I've always approached any chopped variant with these things in mind... and it's partly why I've had good success in getting them to run reliably. While it's true that reducing the spring tension will allow for more impact shock in recoil... with attendant reduced life span for the guns... it should be kept in mind that these pistols were never intended for heavy range use or weekly target shooting sessions. They were designed and for concealed carry and their purpose is strictly business. Their niche is much like alloy-framed, snub- nosed revolvers... "Carried a lot and seldom shot."
Mornin' folks. I have not halted my test with the photos. The weather has been "NASTY" here in sunny southern California!!! Rain every day it seems. More as we speak. Have all the equipment needed, except the weather. I made up 20 "triggers for the flash, so if it works the way I want, I should have some good pictures in the works.
[note: thread continued a while, but no further messages from jpl-labs]