I am no engineer. I am even less engineer than I am lawyer, so I thought I'd put the disclaimer out there up front. Now that it is outta the way:

My XD40 has the captive recoil springs and I know Barstow and Don's make set ups for them.

I just bought a CZ RAMI recently and have heard that an upgrade from the factory springs helps reliability particularly with the .40. The RAMI uses the same spring set as the Kimber Ultra Carry. I ordered the 18lb and the 21 lb sets . .. . It'll be a two recoil spring set in each case and I was wondering if anybody had tried mixing sets in a two recoil spring system. Alternately if any engineer types could speculate -

The range of combinations is 21 lb inner and outer, 21lb inner with 18 outer, 18 inner with 21 outer, and 18 inner and outer . . . . while we expect the 18 set to be an 18lb and the 21 set to be a 21lb . . . what would the combinations be like? 19.5 for both combinations seems too easy. Wondering how it might effect the recoil of the pistol not sure which spring gets loaded first and I suppose that would be a question that'd have to be answered first.

In the Rami the springs sit this way:

I would be leery of trying it. My guess is that it will cause an uneven compression rate and lead to the weaker spring in the pair being overworked and failing sooner than necessary.

Doing that would force the weaker spring to take all of the recoil load (until full spring compression was achieved), and then the stronger spring would take over, instead of both springs compressing at an equal rate....doesn't really sound like a good idea to me.

Would uneven spring rates make a difference? From a practical point of view, car and motorcycle shocks are built this way. Without spending a bunch of time doing research and computerized simulation, wouldn't it just be easier to try it?

I don't know why you should be leery of it. The relatively small changes in spring tension that Macx has proposed, would not be a radical departure from the stock spring (correct?). We all know that the springs will have to be replaced after so many shots fired so decreasing the spring tension could simulate that. What you are doing shouldn't be that different from how your springs perform after a few thousand shots fired.

If it was my carry gun, I wouldn't experiment for the sake of experimenting, unless it was to fix a specific problem. What would be the goal of lowering the recoil spring tension; to reduce wear and tear on the slide or the frame?

The car and motorcycle shock idea was what got me to thinking about it in the first place. I was trying to "logic out" what might yield a progressive spring rate .. .. My RAMI is with Srigs, getting a holster and my springs haven't come yet, so I can't try it.

Would it be the rate or the location that would detirmine which spring would compress first?


Oh, the stock springs on the .40 Ramis tend to be a little weak leading to FTF problems. The 18lb Wolf springs bring them up to the way they should be from the factory and the 21's would be heavier than stock.

Once again, taking my logic from the automotive shocks, I would think that your outer spring would need to be the heavier one. Your maximum compression would be determined by the outer spring.

On further thought, my statement above doesn't hold water, since they are not designed to compress one inside the other.

Very cool. Would that make getting started racking the slide more difficult and it'd get easier toward the end or visa versa? I was thinking the stock spring feels particularly weak near being in battery almost to the point the extractor spring feels strong enough to prevent a shell from loading because it may be stronger than the recoil spring. . . hoping that makes sense. Er, like the recoil spring isn't strong enough near being in battery to over power the extractor so that it snaps onto the rim of the case I guess would be the other way to say it.

Automotive shocks are not a good comparison because you're dealing with a liquid (and valves) in addition to springs.

I am not sure exactly what the "18 lb" and "21 lb" stand for. Is it the spring force when installed in the gun? Or is it the spring force when the gun is at full recoil?

In any case, what you would really need to know, would be the spring rate (ie. lbf/inch) which is how stiff the spring is. From the picture the springs appear to be in a series arrangement... like this.

||-\/\/\/\/\/-|-/\/\/\/\/\-||

This would give an equivalent stiffness of Ke = 1/(1/K1 +1/K2)). You could then compare it to the original stiffness Ke_new/Ke_org. I would expect it to behave more like the softer spring.

Since the "lbs" numbers are probably captive forces, what would happen is that your spring carrier would not "center" as designed. If matched springs looked like this installed.
||-\/\/\/\/\/-|-/\/\/\/\/\-||
Then unmatched ones would like like this or this when installed:
||-\/\/\/\/\-|-\/\/\/\/\/\-||
||-\/\/\/\/\/\-|-\/\/\/\/\-||

Neither one would compress first. They would both compress under load, just the softer one would compress more. An unmatched set would probably work the softer spring more, and the stiffer one less; than a matched set.

On reflection, I think you are correct, the springs are not actually compressing one inside the other.



I'm not 100% sure either but I would take it to mean that the springs would be capable of exerting a force of 18 lbs or 21 lbs when compressed.




Would it matter? Both of them appear to bear against a flat plate (the circular retaining stop on the larger barrel). Also would it matter if both sides of the spring carrier compressed evenly? Does the flat plate between the two springs actually preform a function or is just there to provide a surface for the springs to bear against? I do, however, think that you have a valid point and that both springs should be matched. I am not contesting your logic, ironbear, just asking questions.



While I agree that the softer spring would compress more, I think it would compress first (at least to some extent) before the stiffer spring started compressing, if they were unmatched. If one spring compresses more than the other it might fail first.

Jeff Bergquist also made a point that the softer spring might wear out first. It is a consideration. If one spring fails, you might have a malfunction when it is not convenient.

I'm not sure it would matter.

I haven't had a chance to look at one firsthand, so I am guessing based off the picture supplied; but I think that it more than just a flat plate. I think that the center piece is hollow which allows the smaller spring to slide inside the outer spring, allowing a much more compact solid height. This allows it more "spring" room, in very compact package. It seems to be the only thing that makes sense, for the design. Like this:
|oooooooooo
-/\/\/\/\/\/\/\/\/-|
|oooooooooo

If we look at is statically (since dynamically would require differential equations, which are best left alone on a Friday afternoon. ) If the springs are in series, they both share the load. If I have two springs as shown below, the first with a spring rate of 1lb/in and the other with 2 lb/in, and I put a 1 lb load on them, they will both carry 1 lb. The first (1 lb/in) will compress 1 inch. The second (2 lb/in) will compress ½ inch, for an overall compression of 1½ inch.

|-/\/\/\/\/\/\/-||-/\/\/\/\/\-| <- 1lbs

The equivalent spring rate is then (1 lb)/(1½ in) or 0.667 lb/in. It can be calculated directly by 1/(1/(2 lb/in) + 1/(1 lb/in)) = 0.667 lb/in. The point being that for the arrangement shown, for any load, both springs will carry the same load and compress relative to their respective spring rates.

"Wearing out" a spring is fatigue. Fatigue is worst when the range of motion is wide. In an unmatched set, the softer spring would compress farther than normal, and the stiffer one less. This would fatigue the softer one more, and theoretically wear it out faster. Whether the theory makes a "real world" difference... <shrug>

Thanks Ironbear. That makes sense. It sounds like the combinations wouldn't yeild my hoped for result (the ability to simulate a progressive rate spring). I'll be looking forward to trying out the 18 and 21 pound spring sets and not the combinations.