Vector Mystery Solved!

[1911Tuner]

It came to me in a dream...and a 30-minute drive/45 minute conversation with a retired high school physics teacher confirmed it.
_________________________

Anybody figgered out why the slide moves only when the bullet moves...
and why the slide didn't move because the bullet COULDN'T move when it
was blocked by the rod and screw?

With the rod in place, the thrust vector remained balanced throughout the entire pressure curve. The harder the force acted on the slide, the harder the blocked barrel resisted it. As the pressure came down, so did the force
that resisted movement, and the slide would operate easily. Balance!

Without the rod in place, the bullet is free to move, and when it moves the
vector is no longer equal. The force obeys nature's law and follows the path of least resistance...the slide...and the slide moves. The combined mass of the slide, barrel, and bullet aren't enough to resist the force, and they are drawn backward with the slide, even while the bullet is still in the barrel. If the unlocking and linkdown are correctly timed, the bullet exits just prior to the beginning of linkdown. The bullet exits and the slide completes the cycle because of the momentum that's already established.

Hint: The unbalancing of the force vector doesn't occur instantaneously.
It happens gradually. The bullet, even with the frictional resistance,
is easier to move due to having less inertial resistance to acceleration than the slide. The bullet is screaming toward the muzzle, while the slide
is having trouble getting started. (Objects at rest tend to remain at rest until overcome by an outside force. Heavy objects resist a given force for a longer time than lighter objects.)

This explains why a light bullet at low velocity requires a lighter spring to reliably cycle the slide. It offers less inertial resistance to movement, and hence less opposite force available to move the slide. A heavy bullet resists movement more aggressively, and redirects the force back toward the slide. Remember that the slide tries to move as soon as the bullet starts to move. Momentum begins at that point, even though the slide can't yet move. Stored energy.

How does the vector become unequal? Simple. The bullet offers more initial resistance in its passage through the bore than the slide's inertial mass and the force of the recoil spring. Remember...Prior to firing, the slide and barrel are held in battery only by the tension of the recoil spring, and the locked breech only locks when there is a force acting on it in opposite directions. No force, no thrust on bullet or slide. No thrust, no solid lockup. (If it was truly locked...as with a bolt-action rifle...you couldn't simply rack the slide and unlock it. The lockup is created by the vector of thrust, and only when that vector becomes unequal will the slide operate.) As the vector of force begins to shift and gets the slide going, it gradually overcomes the bullet's frictional resistance, and starts winning the tug of war


If the mechanical connection (upper lugs) between slide and barrel is
removed, the slide is free to move independently of the barrel. here you have the "Straight Blowback"..which operates in exactly the same way as the recoil system, except that it requires a heavier slide and/or a stronger spring to prevent opening the breech while chamber pressure is high.

Why? Because the slide and barrel are locked together for the better part of the pressure curve, slide movement is delayed until much of the momentum has bled off in its attempt to pull the slide and barrel in opposite directions.

So...This gives rise to a new question:

Is the 1911 really a locked breech, recoil operated weapon...or is it actually a delayed blowback? Hmmmm?

Flame suit on!

Tuner----------->Outta here like a John Deere...

 

[Old Fuff]

John Browning will come and make big welts on your head ...

During the late 1890's he took out a series of patents. One was for the "straight blowback" design where, as you said, the breech was held closed by nothing but the slide's mass/weight and recoil spring. The other three patents involved some kind of mechanical interlock that kept the slide and barrel locked together until the pressure curve dropped. While the unlocking sequence started when the primer went off and the bullet started to move, some kind of mechanical lock or block (such as lugs on the barrel) provided a "solid" lock (if I may call it that) during the time the bullet was moving down the barrel.

"Delayed Blowback" usually referred to some kind of friction lock, (such as a threaded chamber), where temporary pressure between certain moving parts (including the cartridge case) delayed the movement of the slide or breechblock. Thus the actual locking effect was sometimes doubtful.

For an example of “delayed blowback†consider Colt’s .38 Special Gold Cup target pistol with a threaded chamber.

Flame suit indeed ...!! A-10 Warthog is taking off ...

 

[1911Tuner]

Warthog

I ain't askeered ...All I gotta do is keep duckin' and runnin' until the thrust vector throws that A-10 into a stall...Then I got me a 30mm cannon to
play with. To the victor goes the spoils!

Bring it on! Tuner<-------Locked and Loaded...

 

[NMshooter]

Well, off the top of my head, the HK roller "lock" system is a pretty good example of delayed blowback. I guess the Walther/Beretta "locking wedge" might be also. However, I could be wrong. (considers A-10, looks around, sees hole, jumps in and pulls hole in after)

 

[Old Fuff]

Tuner ...

You don't have a chance, boy ...

Them A-10 pilots are good, and this one is looking to get your genuine Colt one-piece, all steel, 1911 trigger ...

These guys sometimes fly out of Fort Huachuca, and go low right over my cave ...

Why do you think I live in that cave ... ???

 

[1911Tuner]

Game of Chance

Fuff said:

You don't have a chance, boy ...
________________

Ah'm ya Huckleberry...


Bring'em on!

Edit: Movin' this one over to where the other two are. Nothin' like a good flame war on a Saturday night!

 

[Andrew Wyatt]

so, what you're saying is, with nothing coming out the end, there wasn't any recoil to operate the action.

 

[1911Tuner]

Nuttin' from Nuttin' leaves Nuttin'

Andrew said:

so, what you're saying is, with nothing coming out the end, there wasn't any recoil to operate the action.
-----------------------

Nope. I'm saying that in order to have recoil, the bullet has to move. It
can stop before it gets out of the muzzle, and still produce recoil...it just won't allow a complete cycle. If the bullet doesn't move,(action) there can be no equal and opposite reaction. Unlocking can't occur until the bullet leaves the muzzle though...The forward"pull" on the barrel has to stop
before the mechanical connection between the barrel and slide can be broken. The only other way is to have no force acting on either one...Then it can be hand-cycled.

Demonstrate by cobbling up a squib load and firing it. About one
grain of Bullseye with a wad of cotton on top to keep it in the bottom of the case should leave the bullet in the barrel. The slide will move...
it just won't move very far.

Be prepared to drive the bullet out when you're through.

 

[denfoote]

These guys sometimes fly out of Fort Huachuca, and go low right over my cave ...

Fuff,
That ain't nuttin!!
Right after 911, the AF guys from Davis-Monthan were flying combat air patrols over Palo Verde!!! Well, to make a long story short, some fool decided to take his chopper ( I think it was your Army folks) up for a spin in the vicinity and, as a result, we were treated to a low level (I think it's properly called "treetop" level) pass by two F-16's right BETWEEN units one and two!!

Now, that was a sight to behold!!!

As touching the force vector question, my tensor mechanics is so rusty that I probably, in the words of Capt. Bart Mancouso USN Ret., would calculate the dimensions of the Playmate of the month!!!

 

[RJ357]

1911Tuner -

You cannot store momentum unless there is an increase (a change) in velocity. A continuous force on a nonmoving object does not add any momentum to it.

 

[Andrew Wyatt]

I'm saying that in order to have recoil, the bullet has to move.

Replace "bullet" with "bullet and other ejecta" and you'll have said what I just said.

 

[sm]

I've perusing the Physics Tutor Site Tamara provided . I never had Physics - well other than what little publik skool tossed out.

Right now in College I'm taking the Electronics stuff. IT related. I hope to test some old monitors and laptops. My experiment - which is more effective against monitors - All steel handgun, polymer handgun , semi vs wheelie....all in the name of IT research of course

On this 1911 , Vector , and Physics ....I'm waiting for the Cliff Notes - pics/ videos and whatever else it takes. Yeah - I admit , I ain't that smart - but you folks knew that already .

This has / is most facinating and educational. I really do appreciate the time and input of everyone. I have a lot of respect of folks here on THR/ TFL already, my respect for folks went up a bunch of notches...

 

[NMshooter]

Incidentaly, try taking a length of pipe, put a charge of powder in the center, and load a bullet or ball in the "front", with an equal mass of sawdust or plastic pellets in the other end, and set it off. "Recoilless" gun. If you don't want to use a "countermass" multiply the powder charge by four and you should get about the same muzzle velocity.

 

[Tamara]

I hate to summon this from the dead, but I was lost in thought today and it suddenly burbled into my head that, in addition to well-known recoil and blowback actions, there are also blow-forward actions, where the breech is fixed and the barrel carries forward with the bullet momentum/cartridge blast. Lack of an easy way to ensure reliable ejection and complex mechanisms kept them from ever catching on, but they did exist. I believe that it was used as recently as the immediate post-WWII period by the Swiss in an assault rifle design.

How's this relate to any previous calculamations?

 

[shoobe01]

Bloq forward is reputed (patents or something by the makers) to use the friction of the bullet... the physics of this always seemed suspect to me.

Blow forward comes up once in a while. It seems one of the 40 mm launchers around viet-nam era (from whence we got the M203 and Mk19) was blow-forward in some way. And maybe a shotgun in the last 10-20 years?

The rifle you are thinking about is the Sig 503, 53.. something like that. Seems like it had full wood and a curved, AK like magazine and fired some abbreviated cartrdige. Its in Ezell's book I think, if anyone wants to look it up. I don't think it was made in quantity, but could be wrong.

 

[Grump]

Remember that the slide tries to move as soon as the bullet starts to move. Momentum begins at that point, even though the slide can't yet move. Stored energy.

Uh, I don't see how it's stored. At those early instants, the energy is imparted and the parts are moving but because of their high mass they have not moved far. The recoiling pieces continue to accelerate as the bullet and ejecta also accelerate in the oppostite direction. Just like the springs in a double-piston airgun...but different in key ways as well...

 

[Hand_Rifle_Guy]

He's at it AGAIN!...

Thou hast proposed a fundamentally disingenous premise, heretic.

Thou shalt indeed suffer for thy presumption. What say you, heretic? Wilt thou confess to thy sin of disbelief? Profess thy true understanding of All That Is Holy?

Recant. Recant thy heresy swiftly, or prepare to suffer the just retribution of the vengeful spirit of He that reigneth over ALL our kingdom...

Recant! Know thy blasphemy offends the ears of the righteous followers of the Holy Teachings of thy Lord and Master, John Moses Browning!

On your knees! Beg for the forgiveness of he that waxeth powerful, and blesseth the humble earth with the devine products of the fertile cornucopia that is the Great Gun-engineer's vital imagination!

Recant swiftly, heretic, for even now the Inquisitors converge on thy humble shop, bearing the holy writ of Kuhnhausen and Cooper to justify any horror in the name of Truth and Purity, and every man will know that All Fall To Hardball, or indeed surely they will suffer his righteous wrath...

Is the 1911 really a locked breech, recoil operated weapon...or is it actually a delayed blowback? Hmmmm?

Why does it smell like brimstone in here? Somebody been messing around with blackpowder? And why is that question melted into the concrete?...

Right. This one's actually easy, provided one can keep one's brain wrapped around the neccessary concepts.

Starting from the end, blowback operation uses the cartridge case as a piston moveing out of the barrel to convey momentum to the slide. The mass of the slide gives it sufficient inertia to resist the rearward movement of said case any significant distance until after the bullet has exited the barrel, which precipitates a VERY rapid drop-off of pressure. This drop-off enables the thinner, weaker top-half of the case to withstand the force of the hot gasses without splitting open, dumping the magazine, hammering the pistol frame, and the shooter's hand!

If the slide was of too great a mass, it would recieve insufficient momentum to cycle the action, if too light, it would allow the action to open too soon, resulting in the catastrophic failure outlined above. A heavier spring could help counteract this, but slide mass is more important, as a lightweight slide and a heavby spring results in excessively high slide velocity and cyclic rates. This makes for feeding issues, snappy, violent recoil from violent frame battering, and peening at the contact points along with premature wear.

With the blowback action, therefore, slide mass is everything. This is why there are comparitively few full-power blowback actions, and the ones that DO exist have MASSIVE slides. Cases in point, the Astra 400 and 600, the .45 caliber High Point with an upper like an oil tanker, the .45 caliber RPB Mac-10 clones that weigh something like 5-6 pounds despite being a folded-up tin box (That contains a huge steel brick!) and the almost-too-heavy-to-be-reasonable bolt assembly of the Winchester 1910 Self Loading rifle in .401 WSL caliber.

Now, our Lord JMB's 1911 does not require such a massive weight to function, nor a heavy spring or complexly-leveraged hammer geometry to resist the initial high-pressure spike at the beginning of it's cycle. This is accomplished by locking the slide and the barrel together. When the pressure is high before the bullet departs from the barrel, the lugs on the top of the slide positively engage the recesses under the hood to form a mechanical linkage. The slide and the barrel are a solid, closed-end tube at this point, to all intents and purposes.

However, the slide/barrel unit can move, some what. When the bullet heads off down the barrel, the much-more-massive slide/barrel gets pushed back. It's velocity is MUCH less than that of the bullet, as it weighs many times more, and it balances the bullets speed in the simple equasion of slide-Mass x velocity = bullet-Mass x velocity.

Here's where we depart from any connection to blowback operation. The time-delay that allows the bullet to exit the barrel, thus precipitously dropping the pressure against the case and breech, comes from the much slower slide/barrel speed. teh time it takes the slide/barrel unit to travel what, all of 3/16", an 1/8"? (Tuner, you oughta know the numbers on this.) straight back is enough to let the bullet exit.

Pressure then drops off. It could go down to zero at this point, as we no longer need any additional energy to cycle the action. The slide/barrel unit, like the bullet speeding downrange, is still moving along with a good dose of kinetic energy, which it commences to tap in order to compress the recoil spring. Having traveled together up until now as a unit, the link on the bottom of the barrel now proceeds to turn the reciprocating motion of the recoiling slide into the rotational motion which changes the direction of the barrel's movement from straight back to straight down against the frame. This pulls the barrel down away from the slide far enough to disengage the mechanical linkage of the barrel lugs to the slide. The barrel slaps to a stop, and the slide, stuck on rails like a train, and as able to steer, continues on it's merry way straight back, compressing the recoil spring on the way to store energy for the re-chambering sequence.

At this point, there's essentialy no pressure exerted on the cartridge case. It is no longer pushing on the breechface. The slide is moving from residual velocity it gained when the barrel was engaged to it's locking recesses. This residual velocity in the slide drags the case clear of the end of the barrel using the hook that is the extractor, until the case-head crashes into the ejector, whereupon the the case is levered out of the gun by pivoting around the end of the extractor and heads off for parts unknown to have a cold one. End of HIS story.

Meanwhile, the slide continues moving back until it clears the top of the next cartridge in the magazine which promptly sticks it's butt of in the air in front the bottom edge of the breechface because of the mag spring. The slide, finally done with everything it needed to do after cocking the hammer, slams to a halt against the frame, or a Shok-buff if there's one there, and transmits what is essentialy the bulk of felt recoil to the shooter. Half done.

Now, if there was no recoil spring, the slide would just sit. Note: the slide was never subjected to velocity derived from the action of the cartridge case acting as a gas-driven piston sliding out of the bore during the whole of the rearward movement. It recieved ALL of it's velocity from time when the barrel and the slide were recoiling together as a solid unit. (Hence the term "recoil operated.") The slide, via the extractor, pulled the case from the barrel.

A blowback action forces the case out from gas pressure, and if it weren't for the neccessity of unloading, blowbacks would not need extractors.

From here out, everything is gravy, and recoil-operated ands blowback systems run essentialy the same while they run forward, strip a round out of the mag and stuff it in the chamber. the only difference is the 1911 barrel is pivoted up by it's link as it's pushed forwards, engaging the mechanical linkage of the barrel to the slide and making the two a solid unit again.

Because the slide/barrel unit can be unlocked late enough to make pressure a moot point, the recoil spring does not have to contend with the large amount of kinetic energy that the blowback gun must handle, so it can be considerably lighter, making the locked breech gun MUCH easier to cock. Additionally, as the frame of the blowback gun, and hence the shooter, must absorb ALL of the kinetic energy of the forward-racing bullet when the faster-moving slide slams into the frame, felt recoil of blowback guns is a LOT more snappy and violent DESPITE their typically smaller caliber applications than most locked-breech guns.

This can be dealt with, but it must be within limits. Absorbing more of the slide velocity into a recoil spring makes for a very difficult-to-cock gun, which reaches a point of diminishing returns very quickly. The only OTHER solution is to increase bolt mass, which makes for a bigger, heavier, and more expensive gun. Thje ultimate end of this direction is the Sub-machine gun whose rifle configuration and larger tubular reciever can accomodate a bigger bolt and springs with ease.

But of course, a sub-machine gun's a LONG gun, and we're talking PISTOLS here, right? (No-one says ONE WORD about Czech Skorpion Machine pistols. Not one, hear me? Besides, those things are a long reach to call a pistol anyway, and they're chambered for the winky .32 ACP, mostly.)


Right. We're out of time, so I'm afraid questions will have to wait until tomorrow's class. For tonight, it's chapters 6 and 7 in the Kuhnhausen book, which we'll go over in class tomorrow. Remember, there's a test coming up Monday next week Covering the first half of the book that's going to count as 20% of your final grade, so make sure you take good notes! I'll be in my office later this afternoon if anybody wants to stop by for questions regarding the reloading assignments due at the end of the quarter, or if you need to pick-up more qualification practice targets...




If he doesn't get it on the first try on THIS one, I'll feed him to the Inquisitors myself...

 

[1911Tuner]

Fire and Brimstone

Why does it smell like brimstone in here? Somebody been messing around with blackpowder? And why is that question melted into the concrete?...
_____________________

ROFL...I tossed that "Locked or Blowback" question into the fray just to see
what it would stir up. I do know that it's not a blowback operation...delayed or otherwise.

H_R_Guy...I understand and agree completely. My only issue was in the theory that the recoil is caused solely by the bullet's movement, without
regard to the pressure of the burning powder gasses. The premise being that if the bullet moved, the slide would cycle even without the thrust vector provided by those expanding gasses...and that simply can't happen. Demonstrate by removing the rifling from a barrel and opening
the bore up to provide a light fit between bullet and bore. Drill a hole in the bullet and attach a cable. Yank the bullet through the bore, and see if
the slide moves. If the other theory is correct, it should move a little...
but it won't. The burning gasses provide the force which accelerates the bullet AND the slide. The slide moves a short distance, and momentum takes over just as the bullet exits and the vector of thrust disappears.

Thus, the case...backed by the slide that is locked to the barrel...provides the base by which the bullet is pushed. The bullet, tightly swaged into the bore in turn, provides the base from which the slide is pushed backward...
even thiugh the bullet's resistance to motion is rapidly changing as it accelerates through the bore. So...the slide pushes the bullet, and the bullet pushes the slide through the vector of force. Once the slide begins to move, its resistance to acceleration diminishes, and its greater mass
overcomes the forward thrust of the bullet that is pulling the barrel forward...and begins to pull both barrel and bullet rearward with it. Momentum in the more massive slide is established, and just as the bullet exits, its stored energy is suddenly loosed...and the slide moves rearward at relatively high speed.

As for the statement: "If there was no recoil spring, the slide would just sit there." I assume that you meant that it wouldn't return to battery
after it slammed into the recoil surface in the frame. (Via the guide rod head) It would bounce forward for a short distance...but it wouldn't return to full battery without the spring.

 

[BigG]

"Delayed Blowback"

We used to call that "retarded blowback." Is it not PC to use that term now, that we had to coin another phrase for something already perfectly described?

 

[Hand_Rifle_Guy]

<dramatic fanfare music.>NO ONE expects the Slabside Inquisition!!!

Boy, those fanatical 1911 guys are just over the top! Fire-and-brimstone flash-bangs, red kevlar robes, armor-steel book-covers on the hymnals...

And those hats. Don't laugh at 'em when they're still around to hear you, lest they take offence and drag you off to a cell someplace for a "confession". Their only saving grace is that they preach that regular shooting practice is good for the soul.

"Church of St. John the Gunsmith". They even yell at the NRA! i think they might even be crazier than ME some days.

"Stirrin' up trouble". Hokay, I can get right behind that. Guilty of that meself on occaision. Sometimes you just gotta poke the anthill...to better focus the magnifying glass, of course.

My only issue was in the theory that the recoil is caused solely by the bullet's movement, without regard to the pressure of the burning powder gasses. The premise being that if the bullet moved, the slide would cycle even without the thrust vector provided by those expanding gasses...

Right. Through all that whole debate, the idea that movement alone, without some sort of medium with which to transmit the energy, was responsible for slide cycling somehow went right past me. It's so entirely counter-intuitive to me that I failed to grasp that concept as a premise that needed debunking. Also painfully obvious to me was the idea thrust applied against inertial resistance worked both ways in a balance of forces, which is not neccessarily as automatically intuitive to the rest of the world.

Well, that's old hat. 'Swhy I have tendency to irritate folks. I take for granted a presumed level of understanding that's not always present, and come across as pendantic or patronizing or worse yet, deliberately insulting of intelligence, which is about the furthest thing from my intentions as one could imagine. It STILL catches me off-guard, and I have therefore cultivated a large store of humility and forgiveness in hopes of receiving the same when I finally figure out how completely murky and difficult-to-grasp my thinking is.

It only goes so far. Basically, I'm on another planet most of the time. At least I'm used to being by myself. Who'da thought being a latch-key kid would prove useful? But I digress. Back on topic...

even though the bullet's resistance to motion is rapidly changing as it accelerates through the bore. So...the slide pushes the bullet, and the bullet pushes the slide through the vector of force. Once the slide begins to move, it's resistance to acceleration diminishes,

A couple concepts here I wonder about. First, does the amount of friction from the bore acting on the bullet actually change as a factor of the speed of the bullet's travel? I dunno. I can entertain the possibility, but I have no way to check it.

The second is the slide's diminishing resistance to acceleration, also as a factor of speed. This one I have to take issue with, as niether the mass nor the properties of that mass's inertia are going to change depending on how fast they travel. Presuming no outside frictional interference, (Like air.) I would imagine that the amount of energy required to change from 100 fps to 200 fps is the same as what's required to go from 200 fps to 300 fps. It's just changing position on a number line, relative to the mass itself. That would mean that the amount of difference in delivered energy to whatever the mass next encounters would be the same between examples going 100 and 200 fps and examples going 200 and 300 fps. (Einstein says otherwise, I believe, but that only applies to speeds up near the speed of light.)

However, these quibbles do not invalidate your explanation, they just change the time-sequence and minorly adjust the numbers of the forces involved, so they still all balance out at the end.

Hmmm. Makes me want to make a big complicated graph of acceleration vs. friction vs. pressure curve for both bullet and the slide/barrel, with a side for the shorter, different path the barrel makes after lug dis-engagement, laid out on a timeline that's got a couple feet to the millisecond. That'd take really high-resolution high-speed photography and equally-detailed realtime pressure-transducer info, which I'm not even sure exists for the level of resolution I want. Where's my NASA ballistics lab when I need it? I just had it yesterday...

As for the statement: "If there was no recoil spring, the slide would just sit there." I assume that you meant that it wouldn't return to battery after it slammed into the recoil surface in the frame.

Yup. Got it in one. Pardon my lack of clarity, as I was running around tracking all this realtime data streaming out of my Pocket NASA Ballistics Lab, and I was cutting corners on typing.

I wonder if we oughta cross-link this thread with the rest of the heavy physics discussion. Might be handy thing to have in the Library, too.

 

[NMshooter]

Yes, friction is greater at rest, decreases in motion, does not go to zero. Of course, by the time the friction has decreased due to the motion of the various parts and pieces involved there is enough kinetic energy in the system to make things happen. (lot of moving parts in that pistol, they all have friction)

 

[Jim K]

All of this because some folks just can't grasp the idea that something invisible, like recoil, can actually have an effect. So since recoil, being hard to imagine, does not (to them) exist, something else must operate those pistols. Something that can be seen or felt, like friction or pressure.

Odd, since one natural law that involves an invisible force is taken for granted. If it weren't, people would be jumping off tall buildings all the time to test the "thrust vectors" involved in air resistance, buoyancy, the action of fluids in resisting motion, and so on. But gravity, though invisible and hard to grasp, really does exist, and we know it instinctively and accept it.

If in doubt, try the tall building approach. I will send condolences to your family and tell them you died in the interests of science, trying to prove that a force has no effect if it is not understood.

Jim

 

[Tamara]

Jim Keenan,

If the bullet moving forward causes the barrel to go backward in a recoil operated gun, how does the bullet moving forward cause the barrel to move forward in a "blow-forward" design like the SIG AK53?

 

[1911Tuner]

This Thread...and the Other One

Have been a hoot! I've enjoyed it immensely and look forward to the next one...comin' soon to a forum near you!

Cheers all!

Tuner

 

[niemand]

"Blow Foreward" Designs (By Example; "Schwarzlose") Function from "Standing-Breech" i.e. "Immovable Surface". This effect yet valid with but Temporary "Immovable Surface" (Such as Reciprocating Bolt). Klar?

I note, "Semmerling LM-4" I once converted to Self-Loading function. Process was "Fussy". Function good, exceptionally "Spring-Tension Critical".