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Discussion Starter #1 (Edited)
The information below is from actual measurements of near-new recoil springs from German and Interarms .380 pistols. I don't have a force gauge so I didn't measure the spring rate, but assuming the spring is well-made and correctly heat-treated, these dimensions tell you all you really need to know. It should be understood that these springs were taken out of guns and have already taken some degree of "set", which reduces their overall length; brand new springs in a package may be slightly longer.

I have no idea whether S&W-made Walthers are the same or not.

PP .380, c.1984: wire dia: .051", coils: 16-1/2 total, both ends closed and ground (14-1/2+1+1 coils); OAL at rest: 4.5". Outer circumference of rear coils NOT ground because the barrel boss is not counterbored in a PP.

PPK-PPK/s, German c.1980 and Interarms c.1982: wire dia.: .053", total coils varied from 9-3/4 to 10-1/4, German and early & mid Interarms are closed and ground both ends (8-1/4 [to 8-3/4] +3/4+3/4 coils). OAL 2-13/16" to 3-1/8". Outer circumference of rear coil is ground to fit counterbore in barrel boss.

Barrel boss counterbore was omitted in late Interarms production and rear end of recoil spring is not closed and ground, just snipped off to length. (*see following post). The spring's outer circumference at the rear was left round. Note that the small diameter end of the spring goes around the barrel; the larger end faces the muzzle.

A spring that when installed extends at least 1/2" beyond the muzzle when the slide is removed can be presumed strong enough if the spring is not kinked or obviously lame and the gun is functioning correctly.

A recoil spring that is too long (some S&Ws) or has too many coils, or is made of wire too thick, makes it difficult to dismount the slide and the spring may go "solid" before the slide reaches the end of its rearward travel. If it goes solid in recoil, it impairs the functioning of the gun, overstresses the spring and leads to its early demise.

M
 

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Discussion Starter #2 (Edited)
I have borrowed this from another thread, as it has a bearing on the "clipped" recoil springs found in some Interarms and S&W .380 pistols.

My suspicion --and it's only that; no information to confirm it-- that the reason Interarms introduced clipped recoil springs in PPK/s and PPK .380s might have been because, after the decision was made to omit the barrel boss counterbore to reduce manufacturing cost, it was discovered that the existing recoil springs no longer compressed comfortably in the shorter space available, especially when dismounting the slide. Then it was discovered that a goodly supply of recoil springs had already been purchased, so to avoid discarding them they were clipped to a workable length.

That's only my suspicion, but I can't think of any other reason not to use a closed and ground coil on the rear end of the spring.
If the pistol has a counterbored barrel boss, the correct spring is one with a closed and ground rear coil. If there is no counterbore, the clipped spring is not very elegant but will work provided it is not too long.

I further suspect that that little bit of Ranger's learned experience was not passed on to S&W, who proceeded according to the Walther drawings and did not compensate for the omission of the counterbore. The difficulty in dismounting the slide on some S&W guns results from the fact that the spring "goes solid" before the slide has cleared the frame rails, unless the coils are distorted by brute force into an eccentricity that allows them to stack more tightly. It is unknown to me whether S&W subsequently re-engineered the spring.

Just my suspicion, mind you.

M
 

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I can confirm that in more than (1) S&W PPK/S .380 pistol I've seen, the recoil spring was stronger and longer than the Ranger-Interarms pistols.

This is why you may often hear of S&W PPK/S .380 owners complaining about their slides not closing fully upon firing. This is even with premium (hotter) ammo.

My solution to this (for the S&W pistols) was to swap out their factory spring and use the Ranger-Interarms 20 lbs spring - leading to 100% reliability. (Keep in mind, I still use lighter Wolff recoil springs for Ranger-Interarms pistols as those have a different feed-ramp design.) I can get these "Ranger 20 lbs springs" because I have a few standing by, which I don't use on their intended pistols. Another way of acquiring these springs in parts-bundle purchases from online sources. The 20 lbs recoil spring is often among these parts-bundles.
 

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Discussion Starter #4 (Edited)
I ran across an original Walther drawing for the recoil spring for a .380 PPK or PPK/s, part no. 216 41 83, dated 1969 and last updated 1985. The spring is shown to be 80mm long (3.15"), 8-1/2 active coils + 3/4 on each end, closed and ground. OD at front end is 16mm (-0.5). At the rear where the last two coils are also ground on their outside circumference to clear the barrel boss counterbore, the OD is 14.4mm (-0.2). The wire diameter is 1.35mm (i.e., about .053"). The calculated spring rate is c=152 p/mm.

FWIW: Walther separately indicated that when gauged, the values were within a range of 32 N - 40.1 N. (Not being an engineer, I have no idea what this means.)

M
 

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N = Newton as far as I know.

My little conversion program says this...

32 N = 7.193886 pound force.

40.1 N = 9.014839 pound force.

Neither of which seems meaningful as an expression of spring rate.

I'm no engineer either.

Now, if we use these figures as an expression of energy they seem more realistic...

32 N/meter = 23.601 lb./ft.

40.1 N/meter = 29.57624 lb./ft.
 

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My IA Ranger PPKS has the barrel boss counter-bore, but my IA Ranger PPK does not.
Both pistols are equal in reliability and accuracy, so what was the design purpose of the counter-bore? Do German made pistols have a counter-bore, or was it something IA added?
 

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Discussion Starter #8
... so what was the design purpose of the counter-bore? Do German made pistols have a counter-bore, or was it something IA added?
The counterbore on the barrel boss is found only on the short slide models, i.e., PPK and PPK/s. All such postwar Walther/Manurhin pistols made before the 1980s have it, as do the first few years of Interarms USA production.

It does not appear on PP models.

From this, it may be deduced that the design purpose of the counterbore was to allow a heavier wire-diameter spring to be used in caliber .380 PPK and PPK pistols in order to achieve a desired spring rate. Though it appears also on PPK and PPK/s frames in .32 and even .22, where it is unnecessary because smaller diameter wire is used for the recoil springs, the counterbore may have been standardized for production reasons (e.g., beginning in 1969, many PPK/s .22s were built on frames in the .380 s/n range).

Because larger diameter wire necessarily translates to a longer length when fully compressed, and because the internal space within the pistol for spring compression is limited, a counterbore would provide some extra space into which the spring could compress. Since the slide does not travel as far rearward in recoil as it must to allow dismounting of the slide, the counterbore may have been intended only to facilitate disassembly. As we know, the margin is very tight in .380.

Anyhow, that's just a deduction. I don't really know for sure.

M
 

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MG Mike -- my apologies, but just reading this on on 23 Dec 2014. Thanks for the great explanation. The most recent addition to my staggering collection of two (2) Walther pistols is a very nice stainless steel IA/Ranger PPKS in 380. Serial number is S134201 with a 1995 test fire target year. Have only put 4 mags through it (all flawless). Just noticed two parallel grooves or scratches on the outside of the barrel that appear to have been made by the tight end of the recoil spring which has been cut. I've seen cut springs on other IA/Rangers without the counter-bore. I've got no picture upload capability so I can't show it to you, but have you known of cut recoil springs scratching the barrel?
 

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Discussion Starter #10
... have you known of cut recoil springs scratching the barrel?
Sure, but only when you remove or replace them.

One can minimize or eliminate the scratching by torquing the spring in the opposite direction of its winding to expand the last coil, and copiously lubricating the barrel prior to removal. Also, once the spring is removed, the ragged end can be stoned and polished smooth.

M
 

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Thanks, good tips. The gun is so new the barrel also still has the barely visible circular grooves which make the zipping sound as the recoil spring moves when I rack the slide. I'm hopping a couple hundred rounds will polish off the scratches the cut spring made.
 

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I have borrowed this from another thread, as it has a bearing on the "clipped" recoil springs found in some Interarms and S&W .380 pistols.

My suspicion --and it's only that; no information to confirm it-- that the reason Interarms introduced clipped recoil springs in PPK/s and PPK .380s might have been because, after the decision was made to omit the barrel boss counterbore to reduce manufacturing cost, it was discovered that the existing recoil springs no longer compressed comfortably in the shorter space available, especially when dismounting the slide. Then it was discovered that a goodly supply of recoil springs had already been purchased, so to avoid discarding them they were clipped to a workable length.

That's only my suspicion, but I can't think of any other reason not to use a closed and ground coil on the rear end of the spring.
If the pistol has a counterbored barrel boss, the correct spring is one with a closed and ground rear coil. If there is no counterbore, the clipped spring is not very elegant but will work provided it is not too long.

I further suspect that that little bit of Ranger's learned experience was not passed on to S&W, who proceeded according to the Walther drawings and did not compensate for the omission of the counterbore. The difficulty in dismounting the slide on some S&W guns results from the fact that the spring "goes solid" before the slide has cleared the frame rails, unless the coils are distorted by brute force into an eccentricity that allows them to stack more tightly. It is unknown to me whether S&W subsequently re-engineered the spring.

Just my suspicion, mind you.

M
I cannot seem to locate a "genuine" Walther ground recoil spring for a .380 1966 PPK. Do you have any idea's where I should look?
Thanks.
 
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