What was the reason for using the "keystone" shaped wire for the compensating and operating rod springs?
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What was the reason for using the "keystone" shaped wire for the compensating and operating rod springs?
Well that is one that we have been having friendly arguments over for years - but even the word 'argument' is too strong - we basically scratch our heads. There is much here on the keystone springs and the implementation of the round wire spring (including labor problems, ecetera).
The basic idea of the compensating spring must be gleaned from the fact that it was originally called an "auxiliary" or "auxiliary buffer" spring (The Gastrap Garand by Billy Pyle, p. 148) but not much has ever been mentioned as to the real need, but apparently JCG felt the need for a little extra assistance here (you will have to study up on the several functions of the oprod spring in the Garand). The 'keystone' spring was always considered to be a temporary desing as I understand and even John Garand referred to it as a 'screen door spring' (id, at 151 (huge grin)).
But the reason we scratch our heads today is because of the use of the keystone shaped spring combined with the later type 2 follower rod which lacked the comp spring. This means that the single keystone was either sufficient by itself to do its multiple tasks, or that it was just kind of an interrim fix intended to allow production to continue (due to that mentioned labor problem - Bob did an article on this for the GCA Journal) as the spring was already intended to be replaced in these rifles at the first opportunity. Here is a pic of a 179,xxx rifle that showed up with its original keystone and type 2 rod (no comp spring);
http://www.fototime.com/%7BB50D1206-...1/MVC-001S.JPG
Keystones are described as sluggish in the literature but I have always found them to be more along the lines of a softer and more supple spring (could be the same thing ...). JCG himself questioned their longevity in use, and because of their irreplacability today a collector might be inclined to knock you flat on your back if you rack back his rifle with keystones in it (add amusing story about serial number 2 here ...).
In truth, I think keystones are more susceptible to the heat generated by the design which is what makes them brittle (as with all springs generally) - it is not uncommon to find an original keystone rifle (well, so to speak - take that with a grain of salt ... nothign about keystones is 'common' today) and when the oprod it emptied of its spring it will be in several pieces. By this stage we just don't know to just how much heat the springs have been subjected so we treat them all with kid gloves and most guys refuse to compress an action with a keystone in place.
The above posted photo of the keystone spring on the round body follower rod might give the impression that this was used on the gas trap rifles - which is not correct. The gas trap rifles and some of the later gas port rifles both employed a small compensating spring (3 3/4 inches long) which was used in conjunction with the keystone spring. Only later, in 1940, was the keystone and comp spring replaced by the round wire (Wallace Barnes) spring. Because of problems, the keystone spring was later introduced without the comp spring on a special round body follower.
Serial number 189209 with a S-A 1-41 barrel is one of the last known originals with the keystone spring on the round body follower rod.
Attachment 18348
Thanks for the answers guys, I never knew the "keystone" wire was such a mystery. I'm a little embarrassed I forgotten to look in Pyle's book about the matter. He also gives the only CLEAR description of the operation of the compensating spring I have ever seen, (which saves us another posted question)
The later single spring was longer when they removed the comp spring. They added coils to make up for it. Rick B
I think the M1 op rod spring was probably a pretty hard part to perfect because it was a multi function spring. There are four things that must be kept in mind when designing this type of spring. First is seat pressure, second is rate, third is length of travel before coil bind, and fourth is the number of coils. The seat pressure is the amount of force each end of the spring applies to what ever it rests against. One end of the spring applies a certain amount of force to the inside end of the op rod. This pressure must be adequate to push the op rod forward, strip a round from the clip, and completely close the bolt into full battery. The other end of the spring puts pressure on the follower rod, which in turn forces the follower upward to move the next round into position in the clip. Since seat pressure on both ends of the spring is the same, but the job function is different, this could get complicated, especially since the pressure on the bolt is direct, but the pressure on the follower is through a lever (the follower arm). Spring rate is how many pounds it takes to compress a spring 1" . For instance, a straight wound spring with a 10 pound rate will take 10 pounds to compress the spring 1", 20 pounds to compress it 2", and 30 pounds to compress it 3", and on and on until it coil binds. The M1 op rod spring must have a rate that will increase to the point that it overcomes the momentum of the op rod and bolt and stops the bolt before it hits the back of the receiver, but still travels far enough to strip a fresh round from the clip. The rate though must not be so much that as the gas system wears, or the parts get dry or dirty under combat conditions, it can not push the op all the way all the way back. Length of travel is how many inches the spring will compress before the coils come together and prevent any more movement of the spring. The more coils that are in a spring of a certain length, the sooner it will coil bind, but reducing the number of coils also makes the spring stiffer. Reducing the number of coils also makes the spring more prone to break because each coil must move farther for the same amount of travel. Think bending a piece of wire back and forth until it breaks. The first springs were made of square wire because they were trying to get as many coils as possible into the spring to prevent breakage, and a spring made of square wire is stronger than a spring of the same length with the same number of coils made from round wire, just because there is more material in a square piece of metal than in a round piece of the same length. These first springs, even though made from square wire apparently did not provide the correct rate, so a compensator spring was used. The comp spring was obviously an attempt to end up with a dual rate spring because it is a smaller diameter than the main spring. The smaller diameter would make the comp spring stiffer because it takes less wire to make a smaller diameter spring than to make a large diameter spring. The longer the piece of wire used to make a spring is, the softer the spring will be. The comp spring evidently did not perfect the system, so they eventually left it out and redesigned the follower rod for a shorter single spring, obviously an attempt to get more spring pressure which was still not successful. Eventually they went to a round wire spring with fewer coils than the keystone in order to get a strong enough spring. I expect they went to round wire because it was less prone to break, especially since they had to go to fewer coils to get the desired seat pressure and rate. This is not anything I got from researching M1's, but is just my own theory, generated from my racing experience with valve springs and suspension. Nascar fans will probably understand if they just think "spring rubber" which you hear all the time if you watch NASCAR. All the spring rubber does is to cancel out the movement of one coil of a spring, which reduces the amount of usable wire in that spring, which increases the spring rate which in turn makes the spring stiffer. If I have forgotten anything or muddled it up somewhere I welcome anyone jumping in and straightening me out.
Wow, I finally got an answer that I can understand, thank you! I know SA had a Spring Shop that reportedly could make any spring you wanted. Evidently even JCG could not design one that answered all the requirements you list. When Wallace Barnes finally was able to come up with one that did, Garand was elated.
In the modern realm, only the Glock recoil spring uses a non-round wire in coil form, AFAIK. Anything else that y'all can use as examples that are firearms related?
Aside from durability questions, I would imagine that the keystone wire springs were quite difficult to manufacture in quantity, hard to farm out to sub-contractors, and expensive!
Neat - pretty much Winchester's critiques for much of the design when they were first contacted to make the Garand in 1939 ... in short they said it was not ready for production, and Pugsley said it needed 6 more months at the design table (though what he actually said was not quite so nice ...). To be fair, WRA had their own design that they were promoting - the M1 Carbine - and Pugsely was known to be a real SOB that didn't necessarily play fair (I am hoping for at least a chapter in a book on what Bruce Canfield turned up on this) ...Quote:
Originally Posted by jmoore
This whole era is fascitaing to me as so much of it was guided by the personalities involved and how they played off of each other at their respective instuitutions - it really is a lesson in business and flies in the face of one of my old saws that we will almost never know the real reason for anything. In that way, the study of the Garand is also a study in our culture and how things get done. But just looking at John Garand and Springfield Armory, the Garand is probably one of the last great weapon designs to be done in such a seat of the pants manner - a truly unique individual with a truly great mind for exactly such things - the slow evolution of the design from the early 20's on with prototypes and exhaustive testing open to all including dentists and tinkerers of any stripe - none of it will ever happen again, and it produced one of the very finest desings ever produced.
I have a prototype elevation cap lacking the skirt where the yardage markings ended up. It was found in the garage in a tackle box of John Garands and Scott Duff sold a bunch of this stuff years ago. It is a tiny part that is easily dismissed as nothing more than so much junk in a junk box, but it represents a step in the design that lead to another that lead to another. It was carefully considered though one of but many iterations of that part. I am quite certain that John Garand himself put it in that tackle box, though I can only imagine why it was saved instead of being scrapped.
I have another, an extractor of one of the initial designs. Billy Pyle has one with a little number 5 on it (that he discusses on p122 of his book). Here is that earlier design next to the final version of the part;
http://www.fototime.com/%7B0F2864E3-...dyn=1/0008.jpg
Billy speculates in his book that his is numbered for rifle number 5 (which I got to handle is a super cool rifle!) and it may have been, but that was before Scott turned up a few of these in that tackle box - several marked with a number 1 and one marked with an 'e' - perhaps they were testing different designs in an effort to solve the documented breakage problems on this little part.
Every part of the Garand was like that - going through many changes until it was right, until it performed multiple functions in concert with every other part (just like the springs that started this string). Even these tiniest of parts were as critical to the design as any other part and huge amounts of effort went into perfecting them - it amazes me that someone could grasp, let alone design, all of these little functions of all of these little parts all at one time. As a commercial effort, would Winchester have devoted the same effort, did they even have the resources to do so - to spend years on a design without payback and financial reward, or even the very real possiblity that there might be none if the desing failed to produce a commercially viable result? The one that still amazes me to no end is how on earth did they figure out that there was a resonance causing hammers to chip under the stresses of being fired and that there needed to be cancelled by a little extra counter-weight in the form of a 'pad' at the upper corner of the trigger housing (the very earliest trigger housings were without pads)!!! What??? How on earth did they figure THAT out!?
Springfield Armory is gone now as a firearms manufacturer and a slice of history has ended. This design, the M1 Garand, is the last and even with all of its teething problems it is still possibly the very best of what that system produced, of what any system produced ... all from a Canadian born lunatic who used to flood his living room in the winter so he could ice skate inside ... how American is that.
But then as usual, all this is to the choir - Merry Christmas, chior, and thanks for letting me ramble so far afield and sweep the cobwebs from the corners of my mind again.
AMHO and my very best to all.