Author Topic: Replacing CZ Recoil Springs  (Read 28551 times)

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Replacing CZ Recoil Springs
« on: May 29, 2007, 03:44:59 AM »
The following was posted by Boogaloo, a Senior Moderator, in another forum. The content, which was borrowed from another message chain, is good enough to warrant a place in the FAQ area, too.  Boogaloo tells me that forum member DLEONG originally posted it, so credit for the original work goes to him.  My thanks to both of them.
Most CZ40B owners use either the 18, 20, or 22# CZ75B recoil spring from Wolff, although as Walt said, they have to be cut down to work in the CZ40B.
            The following procedure addresses the particulars of fitting one of these springs to a CZ40B. Apologies to the original author who provided this info since I don't remember who it was -
            Just a quick note: merely ensuring that the slide locks back on an empty magazine does not necessarily mean you have cut enough coils off the recoil spring.
            At full recoil, the rear of the slide's recoil spring housing hits the stop surface at the front of the frame's locking block. This is what limits the slide's rearward travel.
            On the 40B, there is about an additional 1/8" of slide travel between the point where the slide stop engages, and where the spring housing hits the frame's stop surface. If you cut off only enough coils to ensure the slide locks back on an empty magazine, the spring might still compress fully before the slide hits the stop surface. If this happens, the spring essentially becomes a solid tube and absorbs the full brunt of the recoil shock. The spring will be destroyed in a matter of a few rounds.
            To ensure the slide is able to retract fully with a new, modified recoil spring, I would do the following:
            1. Field-strip the pistol; remove the recoil spring, rod and barrel.
            2. Reattach the barrel-less slide to the frame and retract it fully. Use a pencil to scribe a line across the slide/frame seam line.
            3. Remove and reassemble the pistol, using the new recoil spring, and begin cutting off coils from the spring until the scribe marks line up. At this point, remove an additional quarter of a coil to account for heat expansion of the spring during live-firing.
            My 40Bs have cut-down 22 lb. Wolff springs intended for the 75, and both function flawlessly

Offline Radom

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Replacing CZ Recoil Springs
« Reply #1 on: January 02, 2008, 07:40:24 AM »

The Function of Recoil Springs:




When shooting 9mm factory ammunition, changing the bullet weight doesn't normally require changing recoil springs with standard pressure ammunition. The velocity of the load is important, but this is normally only a factor with +P and +P+ ammunition.  




The central ideas behind matching a particular load to a recoil spring are: 1) Assuring proper functioning; and 2) Improving subjective, or felt recoil.




A self-loader requires enough energy to strip a round off the magazine and return the slide to battery. The recoil spring must be strong enough to insure proper function. However, if the recoil spring is too strong, it will cause battering as the slide returns forward. In some extreme cases, the slide can return to battery with such force that it actually rebounds, since the impact of metal on metal causes a "bounce." (Later, I refer to this as "bounceback.") For this reason, the operator does not want to use the strongest possible recoil spring, but he/she wants to match the spring to the load.




When shooting higher velocity ammunition, a stronger recoil spring may be necessary. The idea is that this reduces some of the battering on the pistol, because higher pressure and velocity ammunition will cause the slide to move rearward with greater force and velocity. Theoretically, the perfect recoil spring for a particular load will reach maximum compression as the slide reaches its maximum rearward travel. In such a case, the spring is actually slowing the slide down just before it is jolted by the slide stop. The spring then releases its stored energy, moving the slide forward.




In practice, I am not sure if I accept this theory, if for no other reason than the highest rated recoil springs for the CZ tend to cause the "bounceback" phenomenon I described above. (In other words, something is definitely getting "battered" as the pistol returns to battery.) At any rate, a stronger recoil spring will not prolong barrel life. Due to the nature of Browning-derived locking systems, the locking lugs will receive more punishment, despite the stronger spring. Also, high-pressure ammunition accelerates metal fatigue, particularly in the chamber.




However, a stronger recoil spring does improve the subjective, or felt recoil, for the shooter. This appears to be a function of slower slide travel and a general "smoothing out" of the recoil impulse. In other words, the heavier recoil spring lowers slide velocity, but it does not address the higher pressure associated with high velocity 9mm.    








Although chronographs are available to shooters to measure bullet velocities, lay people have no means available to them to accurately measure pressure. Ammunition and arms manufacturers have found it desirable to establish standards for maximum pressure and the testing procedures used to determine them. In the United States, the peak pressures of commercially sold small arms cartridges are established by an independent non-governmental organization. This voluntary entity is SAAMI: Sporting Arms and Ammunition Manufacturers Institute.




For 9mm Luger (aka 9x19, 9mm Parabellum), SAAMI sets this maximum at 35,000 p.s.i. SAAMI "standard" pressure cartridges in this caliber NEVER exceed 35,000 p.s.i. Typically, the peak pressure of a standard 9mm cartridge will fall in the 27,000 - 35,000 p.s.i. range.




SAAMI has established the "+P" designation for certain popular cartridges. This because many modern firearms in these calibers can withstand higher pressures than earlier versions. In handgun cartridges, these are: 9mm Luger. .38 Special, .38 Super Auto, and .45 ACP. Cartridges bearing the +P headstamp exceed normal SAAMI standards, but they do not exceed the +P standard. In 9mm Luger, +P rated cartridges fall in the 35,001 - 38,500 p.s.i. range.




"+P+" is NOT a SAAMI designation. Ammunition marked "+P+" exceeds all accepted SAAMI standards. This is problematic because the consumer has no idea how high the pressures generated by this ammunition will peak. Shooting so-called +P+ ammunition in any real quantity will still shorten the service life of pistols that can handle it.




The European equivalent if SAAMI is CIP: the Commision Internationale Permanente. CIP maximum pressure for 9mm Luger is similar to SAAMI +P. Commercial ammunition made in Europe that conforms to the CIP standards will be conspicuously marked "CIP." Most of this 9mm ammunition, such as Sellier & Bellot, Fiocchi, etc. seems well within normal SAAMI standards. CIP ammunition does not use the +P designation; all cartridges have only one maximum.




NATO has established its own standards for 9mm ammunition. Since the nominal velocity for NATO 9mm is 1300 fps the peak pressure of this ammunition exceeds SAAMI +P and CIP standards.      






Matching Recoil Springs to Ammunition Types:




Based on my experiences, here are my suggestions for the CZ 75/85 series pistols in 9mm. For .40 S&W (CZ 75B) and .45 ACP (CZ 97B), please see the final paragraph. The symbol # indicates the pound symbol (lbs.)




12# = Light target handloads, swaged lead bullet loads. Some OEM springs may be this light. Most owners shoot standard 9mm factory ammunition with this spring weight and have no problems. This weight may be a little too light for a self-defense weapon; I have noticed that the OEM springs cause jams as they wear out.  




14# = Most "economy" ammunition. Ammunition falling within normal SAAMI standards and most CIP ammunition. This is the nominal weight of OEM springs. This weight would be ideal for the vast majority of 9mm shooters. This weight has the advantage of fitting well before taking its "set."  




16# = Most "defense" ammunition or ammunition at the high end of CIP and normal SAAMI standards. Most SAAMI +P. I tend to favor this weight, if only because the springs last for about 5,000 hot handloads with no hiccups. 16# springs will fit tightly until they take their "set."  




18# = Ammunition at the high end of SAAMI +P and some maximum published handloads. I tended to get "bounceback" in both a CZ-75 transitional and CZ-75B SA with this weight. However, it did make the recoil impulse smoother with this hot ammunition.




20-22# = Theoretically, ammunition exceeding SAAMI +P standards, such as 9mm NATO. In all honesty, I don't recommend shooting overpressure 9mm in the first place. Custom pistols with compensators are better suited to this type of ammunition, not CZs. Realistically, most people would probably use a recoil buffer and an 18# spring in a CZ. I doubt that the 20# and 22# Wolff springs would fit without binding, since they were originally designed for a large frame Tanfoglio.    




The nominal spring weight for the .40 S&W CZ 75B is 16#, which means the OEM springs are probably more like 14#. I would recommend the use of the Wolff 16# spring with the CZ 75B in .40 S&W. Since so-called .40 S&W +P ammunition is best avoided (it also tends to use bullet weights better suited for 10mm), 16# should be ideal for the vast majority of shooters. This is also true of the CZ 97B in .45 ACP. I would recommend the 16# or 18# spring in the CZ 97B, but the 18# is a real tight fit in the .45 ACP pistol. The 18# spring is also likely to cause "bounceback" in these pistols, like the 9mm versions.    




What I Actually Do Myself (Your Mileage May Vary):




In theory, you shouldn't change a recoil spring out of hand, and I don't advocate it as a general policy. However, I've been shooting CZ pistols for about seven years now, and I have changed a lot of recoil springs in those years. If you are at the point where you own one or more CZs and know you will need to replace the recoil springs sooner or later, you might as well standardize on 14# or 16# weight, since the springs are cheaper in quantity.




14# springs will fit in all models without binding or causing any initial problems; this includes the CZ 97B model. 16# springs do not always fit smoothly before taking their first "set" by firing a magazine or two. In other words, you should probably standardize on the 16# weight if you own a .40 S&W or .45 ACP model, since 16# will also work in 9mm. If you only own one or more 9mm models, you have the option of either 14# or 16# recoil springs. The 14# springs are OEM specification and fit better. If you are only going to be shooting bulk 115 gr. ammunition in the pistol, there is no real need for the 16# springs. The 16# springs will last longer with 9mm, and they are more pleasant with hotter loads. Since I shoot mostly handloads and own several different models, I use the 16# spring exclusively.




One trick I have learned is using my 9mm 75B SA as the pistol to "set" the springs for the others. For some reason, it never chokes with a brand new 16# spring, whereas several of my other pistols really bind with a new 16# spring (particularly the 97B).                  



The artist formerly known as FEG...