PM40 Recoil Spring - New vs. Old

[CDW]

Just got my replacement recoil spring assembly in from Kahr on Friday. I went to replace the old one with the new one today and was shocked at the difference. I'm going to try and post a picture, but in case it doesn't work I'll just describe it. After roughly 1300 rounds, the old spring was compressed by nearly 3/4 inch when compared to the new one. So, just in case you were wondering if it is really necessary to swap those springs out, the answer is a definite yes.

On Jocko's advice I also ordered a 20.5 # spring from Wolff gun springs but have not installed that one yet. I'll let you know how that goes when I get around to doing it.

[jocko]

the coil count is the same and that sure looks like alot of compression for 1300 rounds but prooff is in the photos that is for sure. Nice job. I think I will take another look at my PM0 springs. I ahve a bag full of replaceent and I am guility about replacing them like I should.

recoil sprigns are cheap to replace and the best thing one can do for his weapong IMO..

[deadhead1971]

were you having issues (jams) or just decided it was time?

I replace my PM9 springs at 785 rounds. I was not having any problems. Mine was compressed as much as yours.

[wyntrout]

Counting only the front loops of the coils, the left one has 14 and the right one 15. That includes the one at the base.
Wynn

[racuda]

I wonder if measuring the spring length could be an early warning indicator of when to replace the spring for those of us who don't keep up with # of rounds fired?

[racuda]

Counting only the front loops of the coils, the left one has 14 and the right one 15. That includes the one at the base.
Wynn

Yes that extra coil accounts for 1/4" out of the 3/4" total.

[jocko]

probably not.

I wonder if measuring the spring length could be an early warning indicator of when to replace the spring for those of us who don't keep up with # of rounds fired?

recoil springs are designe dto take a set and I would bet tha tif a person installed anew set of springs and let it sit a month and never fired it, that set might almost match what is pictured. That is not an indication IMO of a worn out spring. recoil springs are the cheapest things to replace in ur gun, and they do the most good also when they are working within specs.

Probably some ways to think about replacing springs would be m,aybe brass going further than when totally new, or possable slide not locking back all the time, do to maybe worn springs and the slide moving to fast to get totall lock back. Feedng issues can be attributed to weak springs.

If in doubt indeed replace. I buy um by the half dozen form wolffs and I don't change them near as often as most and I probably should though,just that I kinda keep round count but not round count since last recoil spring replacement. I am a fan of the 20.5# PM9 heavier spring, my theory is that if it takes a set and weakens from shooting I am still 10+% heavier than factory, so I should be able to keep that spring in longer....

[wyntrout]

Too many people are worrying about the number of coils or the length. If the coil is designed for the purpose, then use it and see if it works. The darn things set at a shorter length from compression, but they are designed with that in mind -- duh! Again, if it ain't broke don't fix it. Use the manufacturer's recommendations for replacement as a "guide".

I'll say it again, if it ain't broke don't fix it.

Read this info about this subject from the real experts, Wolff Springs:

Wolff Gunsprings - Firearm Springs for Semi-Auto Pistols, Revolvers, Rifles, & Shotguns

This will answer any questions, authoritatively.

Wynn

[jeep45238]

I wonder if measuring the spring length could be an early warning indicator of when to replace the spring for those of us who don't keep up with # of rounds fired?

Not one bit.

Length of the spring has no effect on the strength of the spring.

The alloy, diameter of the wire, heat treat, stress relief, and number of coils directly effect the strength of the spring.

In my handguns, I replace all of the springs in the guns (including mag springs) once per year, regardless the number of rounds fired. It's damn cheap insurance to make sure the guns I bet my life on function 100%. On all of my pistols, I run factory strength springs. This means that on my 1911 clone, I don't run spring rates that Para Ord put in from the factory. I run spring rates John Moses Browning dictated in 1908.

Running factory designated spring rates are very important when you're dealing with a pistol like the Kahr design, which is on the edge of the envelope in regards to reliability and tolerance stacking.

On my AR15, I've got 25ish mags, so those don't wear down nearly as much. I do differ on spring rate and alloy on my AR. It uses a 10% stronger spring made out of A877 chrome silicon alloy that's been heat treated and shot peened. This setup is good to over 500,000 cycles while retaining 95% spring strength. My extractor spring is A401 chrome silicon heat treated, stress relieved, chrygenically treated steel.


If I could get a hammer spring/mag spring/recoil spring set for my pistols made out of the A877 alloy mentioned above though, I'd do it on all of my guns



Running heavier poundage springs only put more stress on parts of the firearm design that were never meant to take that sort of abuse. It doesn't help keep the gun in battery. Varying spring rates *can* effect where the front sight lands when the recoil impulse is over, but with proper technique, this is minimized like you wouldn't believe.

[jocko]

I can't

Too many people are worrying about the number of coils or the length. If the coil is designed for the purpose, then use it and see if it works. The darn things set at a shorter length from compression, but they are designed with that in mind -- duh! Again, if it ain't broke don't fix it. Use the manufacturer's recommendations for replacement as a "guide".

I'll say it again, if it ain't broke don't fix it.

Read this info about this subject from the real experts, Wolff Springs:

Wolff Gunsprings - Firearm Springs for Semi-Auto Pistols, Revolvers, Rifles, & Shotguns

This will answer any questions, authoritatively.

Wynn

hear you:7::7:

[CDW]

I was starting to have FTF's and had a couple instances where the slide failed to lock back. Also, I noticed that all my ejected brass was creased on the side causing the mouth of the case to be deformed into an oval shape. I have not been to range yet since replacing the springs, so don't know if all the issues have been corrected or not yet. As far as the springs taking a set upon installation, you may be entirely correct. I will say that with the new spring in there it is noticeably harder to rack the slide. It feels like a brand new pistol again.

My intention was not to freak anybody out. I just thought it was interesting. I will be replacing my springs at the recommended frequency for sure.

[frank_drebin]

My PM40 has the old spring set from 2007 and the recoil spring is short like the one on the left. I was sent the new one last week and it's long like the one on the right. It's almost impossible to assemble it with the new spring and I don't think it's correct for my model.

[jocko]

I bet it is

My PM40 has the old spring set from 2007 and the recoil spring is short like the one on the left. I was sent the new one last week and it's long like the one on the right. It's almost impossible to assemble it with the new spring and I don't think it's correct for my model.

I just put a new spring in my PM9 and it was a real bugger to get in also. Let the gun sit a week with the new spring and it will take alittle set and you will be OK, but a new spring is a challenge to be sure