RECOIL SPRING

THIS IS A TECHNICAL EXPLANATION OF THE RECOIL SPRING DESIGNER
AS RESEARCHED BY ENGR. SANSIN G. DIO, RME ICML OF SANSIN ENTERPRISES

The Magical, Marvelous, Mystical recoil spring. There are probably more misconceptions--and misinformation--surrounding the application of recoil springs than in any other area of the 1911 design with the possible exception of ramp and throat geometry.
I often hear the question: "What weight recoil spring should I use for Plus P ammo?" And, about as often, I hear erroneous statements to the effect: "You need a heavier spring to handle the pressures."
The answer to the first is a bit involved, and requires more information than just the indication of working pressure levels. Bullet weight and chronographed velocity is more important than pressure.
The response to the second is usually better addressed with an explanation of the way the 1911 and all locked-breech, recoil-operated weapon systems work. I'll make a flat statement and let the readers ponder on it for a minute.
The recoil spring has not one thing to do with containing chamber pressures, and stepping up to a high spring rating will often cause more problems than it solves. Neither does it have any real effect on the barrel unlock timing. In fact, the mainspring has more effect on the barrel and slide timing than the recoil spring does. There's also the matter of the geometry of the firing pin stop...but that's a subject for another discussion.
The recoil spring is captive in the spring tunnel with a fairly light pre-load that comes from the small amount of compression required to get the plug into the end of the tunnel. With a 16-pound rating on the spring, this pre-load amounts to about 3 or 4 pounds. Stepping up to a 20-pound rating increases the pre-load about 25% at most, which would produce a pre-load of 5 pounds. Very little difference, and one that you'd be hard-pressed to feel by hand cycling the slide one-tenth of an inch. Why just a tenth of an inch? Because that's about how far the slide travels when barrel unlocking begins. To further understand this aspect of the operation, it's best to look at the first part of the firing and recoil sequence step-by-step.
The round fires, and the bullet accelerates through the barrel. The barrel is locked to the slide via the locking lugs. Recoil begins with bullet movement, and the slide moves rearward, pulling the barrel with it. The two remain fully locked for a short distance: the one-tenth inch mentioned above. At that point, recoil momentum is established, and the slide will continue rearward to complete the recoil cycle but, more importantly, the barrel begins unlocking and linkdown at the one-tenth inch mark. And some guns start the sequence a little before that. By the time the barrel starts to unlock, the bullet is long gone and chamber pressures have fallen to nearly zero. It's easy to see that with so little slide travel, that any effect that the recoil spring would have is pretty nearly inconsequential.
When addressing the matter of any spring in the system, it's important to remember two things. Springs work both ways, and whenever a spring rate or load is changed, it affects other aspects of the cycle in areas not directly under the influence of the spring. A perfect example is the effect that the mainspring has on the slide's speed and timing. It's entirely possible to set up a pistol to function perfectly with a 10-pound recoil and 17-pound mainspring for reduced velocity target ammunition, and cause the gun to short cycle by simply switching to a 25 pound mainspring. By contrast, you can install an 18-pound recoil spring to reduce frame battering, and drop to a 17 or 18 pound mainspring and completely negate the high-rate recoil spring's benefits.
Now...on to the negative side of recoil springs with high load ratings.
Heavy recoil springs mean slower rearward travel but faster forward travel. The total cycle time changes very little, if at all. All the heavy spring does is alter the balance. Faster forward means that the magazine has to be in top form to keep up, especially on that critical last round...AND...slidelock. I've seen pistols fail to lock on empty nearly every time with an 18 pound spring, then turn around and function perfectly every time when the spring rate drops to 16 pounds.
Faster forward means increased momentum for the slide. When you consider that the relatively small lower lug feet and the slidestop crosspin are the two parts that bring it all to a sudden halt, it's not hard to figure out that if the slide's momentum is increased by 10%, then the shock against these parts is also increased by 10%. That's not a lot if the pistol sees limited use...but in a hard-duty range gun, it means something. The impact surface between slide and frame were designed to withstand a lot of impact shock. The lower lug feet weren't. This is why the dictum to never let the slide go to battery at full speed on an empty chamber is generally accepted wisdom. The feeding phase slows the slide and softens the blow. When the gun is empty, the feet slam into the slidestop crosspin with all the impact that a 16-ounce slide that is driven by the recoil spring can muster. Think of it as slapping the faces of two 16-ounce hammers together at the same speed of the free-moving slide. It won't be long until the hammers begin to deform.
The springs in the 1911 were determined by John Browning and a team of engineers at Colt nearly a century ago. Whenever we start playing around with these carefully considered rates, we very often bring on problems with the gun, all of which may not be immediately apparent.
Any time that a component of a successful design is altered or changed, it affects several aspects of the design's function. The engineer's dictum states that: "Whenever one thing is changed, it usually requires change in at least two other areas in order to compensate for the first change."