Spring Rate Musings

Discuss the FN Five-seveN line of pistols and accessories.

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DoubleJ
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Spring Rate Musings

Post by DoubleJ » 15 May 2016, 14:11

Ever since I got my EA tuned EFK threaded barrel, I've been struggling with excessive shoulder movement. I was hoping it was some odd break in issue, and not a chamber issue. A friend suggested it may be a spring rate issue, but I thought as it was a new, EA heavy spring, that shouldn't be the case. On his advise, I decided to check it out anyway.

According to Hooke's law, so long as you don't over extend a spring with excessive weight, it's rate of stretch (easier to measure) should be directly indicative to it's rate of compression (not so easy to measure).

I took 3 of the 4 springs I own (forgot about the fourth one, so it got excluded) and measured their resting length.

Factory FN spring: 12.5mm
EA spring: 11.4mm
EA spring included with EFK barrel: 11.0mm

I then suspended each spring with a 2.5# weight attached to it.

Factory FN spring: 14.1mm
EA spring: 13.4mm
EA spring included with EFK barrel: 12.9mm

What I found here is that the factory FN spring had both the longest resting length, and only stretched 1.6mm, indicating a higher rate.
The EA springs both stretched 1.9 and 2.0 mm respectively, with resting lengths within .4mm of each other, but 1.1 and 1.5mm shorter than the FN spring.

I installed the factory FN spring onto the EFK barrel, did some shooting today, and my shoulder movement is back to normal, and maybe there's a slight recoil increase, but that could be make-believe in my brain.

Just for S+Gs, I put my Axiom on the FsN and fired some rounds, and shoulder movement increased dramatically, but that's not a surprise. Suppressors increase back pressure and dwell time.

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panzermk2
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Re: Spring Rate Musings

Post by panzermk2 » 16 May 2016, 09:17

You can't stretch test a compression spring. We also use different diameter wire so using just length is not going to work.

Also shoulder movement is totally normal,and with our higher rate spring you will see an increase in performance.
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DoubleJ
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Re: Spring Rate Musings

Post by DoubleJ » 16 May 2016, 14:03

panzermk2 wrote:You can't stretch test a compression spring. We also use different diameter wire so using just length is not going to work.

Also shoulder movement is totally normal,and with our higher rate spring you will see an increase in performance.
Please cite your source, this contradicts everything I've come to understand about Hooke's law. I'm no spring engineer or metalurgist, so I may be wrong, but my research seems to indicate that springs spring either way.

I also measured the three springs I have laying around for wire thickness.

.051
.0505
.052

Max spread of .0015"

Shoulder movement is totally normal, I agree, drawback to a bottleneck cartridge in a straight blowback action. The shoulder movement I was seeing prior to yesterday was alarming to the point that I pulled out old brass (hot reloads, 3x sized and fired) and compared it to 1x fired SS197. I'd guesstimate .040" difference without getting my comparitor out.

With the FN spring back in the gun, shoulder movement is visually identical to old fired brass from the factory barrel/spring combo.

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Re: Spring Rate Musings

Post by Rapier1772 » 17 May 2016, 04:01

DoubleJ wrote:
panzermk2 wrote:You can't stretch test a compression spring. We also use different diameter wire so using just length is not going to work.
Also shoulder movement is totally normal,and with our higher rate spring you will see an increase in performance.
Please cite your source, this contradicts everything I've come to understand about Hooke's law. I'm no spring engineer or metalurgist, so I may be wrong, but my research seems to indicate that springs spring either way.
Got mags?

Take apart your mag & compress the spring, it bounces back. Now stretch the spring, it will likely stay stretched a bit.
At least, that's what happens with mine.
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DoubleJ
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Re: Spring Rate Musings

Post by DoubleJ » 17 May 2016, 04:08

That sounds like the over stretching damage I read about. They can only be compressed until the coils bind, which they're designed for. They can be stretched until they're a straight wire, obviously not useful as a spring any more.

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Re: Spring Rate Musings

Post by panzermk2 » 17 May 2016, 08:12

My source is the guy who makes my springs on a CNC spring manufacturing machine.

He has different types of test stands to test to springs for this reason. How can you spring this spring in both directions?


Image

You can't because springs are designed to work certain ways. These are designed to be compression springs. Also the materiel they are made of is different then factory springs.
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DoubleJ
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Re: Spring Rate Musings

Post by DoubleJ » 17 May 2016, 14:41

That's not the style of spring we're talking about.

You said above the wire was thicker. It isn't. Now it's a different material?

So you called your spring guy, had him check out my findings, he said "BS", and then you replied? Get your spring guy on here, and let's get some science involved that refutes my findings.

Please also keep in mind that I'm your customer. Instead of arguing with me, you should be working with me to find out why my shoulders were being blown out so far. I've mentioned it to you on several occasions on this forum, hoping you'd reach out and help me figure out the problem. $1000 pistol with a $380 barrel on it should be performing better than it was, not worse. This thread was intended to be observational, not combative or accusational, but I'll probably end up being the bad guy that dared to do anything other than fawn over all things EA.

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Re: Spring Rate Musings

Post by joe_r95 » 17 May 2016, 16:53

You're measuring how its performing based on shoulder movement of the casing. Not cycle rate, ballistics, or anything else handguns are normally measured on. From the sounds of it the spring has been lightened(pretty common with handguns) decreasing the time the casing spends in the chamber allowing the neck on this particular cartridge to expand. That should also reduce recoil and increase potential rate of fire. Ferraris burn more gas, but get there faster. You've got to give up something for performance.

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Re: Spring Rate Musings

Post by DoubleJ » 17 May 2016, 18:20

Semi auto, rate of fire is limited by my index finger. Not sure what the P90 runs, but I'm sure I can't match it. Shoulder movement is one of the ways you use to determine pressure in the FsN, it doesn't act like a normal cartridge when working up loads. Primers flow with AE factory loads. If your shoulder movement is excessive, then you're just guessing when reloading, and this isn't the pistol to be guessing with. None of the springs has been modified, all square on both ends.

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Re: Spring Rate Musings

Post by joe_r95 » 17 May 2016, 19:17

Right. You have increased pressures due to the length of the barrel, and shoulder length increases due to the higher pressures. Now you have to deal with the higher pressures without causing a catastrophic failure. Reduce pressures a hair faster? Dont compare the handgun to the rifle. Longer barrel has higher pressures that cause the shoulder to expand....

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Re: Spring Rate Musings

Post by Buffman » 17 May 2016, 19:31

What's the rounds you're using in the gun? Pictures of said shoulder movement?

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Re: Spring Rate Musings

Post by DoubleJ » 17 May 2016, 20:12

Buff - AE, 197, and handloads. I'll see if I can dig out some previously fired brass and get some clear photos. Hopefully I can find the brass from my casting experiment a while back, my velocities never even got to modest, and my shoulders were pushed out like I'd run 55s at 1800. Edit: Looks like I processed all my brass over the winter.

Joe, my only comparison of the P90 to the FsN was rate of fire, as the P90 is fully automatic, and the FsN is not. I'm not Jerry Miculek. I can't shoot anywhere near the rate of a machine gun, nor would I want to. Pressures, shoulders, primers, ballistics, springs etc have no bearing on the rate of fire of a semi-automatic pistol, it's completely controlled by how quickly I choose to operate the trigger. There is also very little difference in my testing of shoulder movement between a PS90 and the FsN. In fact, if I remember correctly, shoulder movement isn't a very good indicator of high pressure in the PS90, smokey loads and magazines coming unlatched are the indicators that you've gotten hot. Either way, this thread is about the differences in spring rates between a few different springs I own, and this isn't my first rodeo with bottlenecks in straight blowback actions, springs rates, and even playing with action weights.

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Re: Spring Rate Musings

Post by joe_r95 » 18 May 2016, 03:50

Yes, recoil springs do have an impact on possible rate of fire whether or not you shoot fast. I was comparing it to a performance upgrade, and also a way to build/relieve pressure. You have a chrono? Take a few measurements with factory loads between the few springs. Higher velocity should equate to high pressure. Either way the only way to measure a compression spring is with a spring compression gauge. I guess you could try to take a fish scale and measure what it takes to rack the slide.

To my knowledge the ps90 operates on a direct blow back system, and the fsn is a delayed blow back, Thats why you cant compare the two. Over pressure in a ps90 comes out with the casing. Over pressuring the fsn results in damaged brass and guns.

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Re: Spring Rate Musings

Post by grimmond » 20 May 2016, 07:21

Joe_r95 go back to the beginning of the post and reread what he said. You are missing the whole point of his post. Enough of the BS. The results he is having is being caused by a faulty spring. And as a fact you can compare the shoulder movement between the 2 springs as fact of an issue. With the HD spring being that it has a heavier weight rating, holds the chamber closed longer which results in less shoulder movement then the factory spring. So using the exact same load a factory spring will have more movement. I have done a compression test between my springs and found that my HD spring has worn out (it compressed at 16lbs) and needs replacing after having fired approx 5000rnds. I do not have a new HD spring in my hands yet to further compare compression to see if it matches spec. My HD spring has worked as advertised from the beginning and since I have not been doing heavy loads did not notice the spring degrade to the point it has. Springs do have a useful life span. DoubleJ's is new and should not be performing like mine yet. This is an closed issue that Jay and DoubleJ need to come to a solution on together.
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Re: Spring Rate Musings

Post by bruteandbear1 » 20 May 2016, 15:24

grimmond wrote:Joe_r95 go back to the beginning of the post and reread what he said. You are missing the whole point of his post. Enough of the BS. The results he is having is being caused by a faulty spring. And as a fact you can compare the shoulder movement between the 2 springs as fact of an issue. With the HD spring being that it has a heavier weight rating, holds the chamber closed longer which results in less shoulder movement then the factory spring. So using the exact same load a factory spring will have more movement. I have done a compression test between my springs and found that my HD spring has worn out (it compressed at 16lbs) and needs replacing after having fired approx 5000rnds. I do not have a new HD spring in my hands yet to further compare compression to see if it matches spec. My HD spring has worked as advertised from the beginning and since I have not been doing heavy loads did not notice the spring degrade to the point it has. Springs do have a useful life span. DoubleJ's is new and should not be performing like mine yet. This is an closed issue that Jay and DoubleJ need to come to a solution on together.
Grimmond, your right on the money! Everyone makes mistakes and DoubleJ just needs a new HD spring shipped free of charge, end of story!!!

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Re: Spring Rate Musings

Post by CPTKILLER » 21 May 2016, 06:12

Spring rates and manufacturers are not a subject for amateurs. As such always go with a firm in the biz who knows springs.

If unsure about spring rates, ask and avoid disappointment.

I'm a retired engineer and 90% of most engineers are clueless.

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Re: Spring Rate Musings

Post by Rapier1772 » 21 May 2016, 09:11

CPTKILLER wrote:I'm a retired engineer and 90% of most engineers are clueless.
Hey! I'm an engineer & I resemble that! :laugh:
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Re: Spring Rate Musings

Post by panzermk2 » 10 Jun 2016, 12:09

DoubleJ wrote:Ever since I got my EA tuned EFK threaded barrel, I've been struggling with excessive shoulder movement. I was hoping it was some odd break in issue, and not a chamber issue. A friend suggested it may be a spring rate issue, but I thought as it was a new, EA heavy spring, that shouldn't be the case. On his advise, I decided to check it out anyway.

According to Hooke's law, so long as you don't over extend a spring with excessive weight, it's rate of stretch (easier to measure) should be directly indicative to it's rate of compression (not so easy to measure).

I took 3 of the 4 springs I own (forgot about the fourth one, so it got excluded) and measured their resting length.

Factory FN spring: 12.5mm
EA spring: 11.4mm
EA spring included with EFK barrel: 11.0mm

I then suspended each spring with a 2.5# weight attached to it.

Factory FN spring: 14.1mm
EA spring: 13.4mm
EA spring included with EFK barrel: 12.9mm

What I found here is that the factory FN spring had both the longest resting length, and only stretched 1.6mm, indicating a higher rate.
The EA springs both stretched 1.9 and 2.0 mm respectively, with resting lengths within .4mm of each other, but 1.1 and 1.5mm shorter than the FN spring.

I installed the factory FN spring onto the EFK barrel, did some shooting today, and my shoulder movement is back to normal, and maybe there's a slight recoil increase, but that could be make-believe in my brain.

Just for S+Gs, I put my Axiom on the FsN and fired some rounds, and shoulder movement increased dramatically, but that's not a surprise. Suppressors increase back pressure and dwell time.

It also appears through my PM's with grimmond that you never recieved the email I sent through the forum asking for your info so I could get you a call tag to get this spring back and replace it with a new one.

I sent it and after that promptly moved on NOT following up with another email. That was a mistake on my part and I apologize.


PM me with your email that you used to order so I can get it replaced.
Jay Wolf
Pr. Elite Ammunition

"Engineers, the oompa-loompas of science!"

Be'ein Tachbulot Yipol Am Veteshua Berov Yoetz
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