Educate me-Flat wire vs round spring technical data...

[opngrnd]

I run the Vltor A5 with everything I can. It's always been as simple as ordering a Green spring when I buy a kit to do a build, and my rifles run very well this way. You could even say that I build the rifles around the A5H2/Green spring combo, since it's worked from -20 to 101 degrees for me. My 18" precision rigs get the A5H3/Green spring. In a recent thread there was discussion of using the flat wire spring instead, with it's own set of benefits and retractions. Knowledge wanted...

[Krazykarl]

Definitely need more information as well. Thank you!

[Motivated1]

Definitely need more information as well. Thank you!

Yes! If Tom, Buford and all SME could contribute, it would be greatly appreciated.

[grizzman]

I'm also interested in this information.

[tom12.7]

So maybe we start with how the product has changed since it first entered the market?
When the spring was first introduced to me, when it was relatively new, I decided to test some out. At the time I was informed that for 5.56 there was a carbine action spring, that could work on some 5.56 rifle actions. A .308 spring that worked with AR-15 carbine buffers with the 3/4"ish extended carbine RE for .308, rifle actions in .308, and some 5.56 rifles.
I already had a low friction set up to test spring loadings from an earlier project. Very simple with a load cell, force screw, and 3 polished rods (to simulate the RE diameter). The testing on the fixture looked great, some more L1 with very similar L2 with the carbine spring. I tried the spring in many known good platforms, the results ended up being erratic. After some more testing, I was looking at what appeared to be friction dragging the action down. I altered my original fixture so that I could check for drag by using a pusher rod down the barrel of an assembled rifle minus the bolt so that the pusher rod was seated to the carrier to test in compression and rebound. The findings were that there could be much more drag in some systems than others. Additional testing was done, the flat wire could add friction that normally wouldn't be there in a conventional spring. There was combinations that worked well, but the flat wire spring was less tolerant to combinations of factors, offset and angular misalignment for the RE, RE interior finish, etc.. There was a coating on the springs, but no amount cycling could make a marked improvement in some with issues, others seemed fine.
A similar test was done slightly later on with the longer version of the spring in rifle actions. Their marketing indicated that cutting coils to trim the spring could be used for tuning. Personally, I'm not a fan of an end user attempting this. I very much believe that springs for this need to be properly closed and ground square, anything else adds an angle to that portion of the spring. That makes more drag on a regular spring, adding that to a flat wire spring adds insult to injury. Cutting the springs down could hurt L2 tensions to the point that the safety margin diminished for stripping the round out of the magazine to chamber. Masking friction issues by reducing the work required to cycle the action isn't a good place to be.
There were combinations that seemed to work well enough, so more testing was done. When the drag was low, the springs showed benefits. Around this time, I was able to get with an engineer that actually worked on springs. He wasn't fast about getting back with me, it took him over a year. During that time I continued with the combinations that seemed to work well and relegated the others back to normal springs.
In some of my "good" flat wire combinations, issues came up. Symptoms started as erratic forms of function. Upon removing the springs, it was evident that some coils towards the buffer became kinked. Not long after, those springs would break. I wouldn't run a broken spring, even if there was some function, so those combinations were out.
A few others, mostly suppressed guns started to show signs of corrosion on portions of the spring.
Around this time, my spring engineer guy got back with me. When he told me the stress level range compared to a normal spring, I understood that the spring had 50% more stress than a conventional one. I still had some combinations that seemed to work well, so I continued to test. The springs with rust would fail fast and would break in multiple locations. During that same timeframe, I had the opportunity to test some cut away guns on camera. I was not and am not opposed to the concept of the L1 and L2 tensions of the flat spring, more of the offering's execution of that. What was found in the camera findings was how tightly the springs coils could stack together quickly during the action sequence towards the buffer end. The shock loading of the spring during initial movement was shown to my spring engineer with different amounts of gassed uppers using different buffer masses. The lower mass shock loaded more than than the higher mass options and he really questioned the L1 loading with the action at higher velocities.
At the end with the issues of drag, breakage, rust, shock loading, etc.. I gave up on how the spring was done, not the concept of the increased L1 with similar L2 for this system. Pneumatic systems showed that years prior, but carrying an air tank with hoses is not practical. While in typing, the process explained may seem exhaustive, but it was not out of my normal during that timeframe doing what I was doing.
This is by no means to condemn or discourage others from trying the product, as their execution of this has improved by a great deal at this time. It's not a jack of all trades by now, but a master of some. The product has improved in time, and I am glad to see that. There are some other issues that could be addressed, but it is good to see how the product has improved over time.
More to follow if interested.

[Krazykarl]

Fantastic work! Could you define L1 and L2 please? What sort of service life were you getting out of these springs? Was there a gradual and predictable reduction in spring force or sudden drop off?

[hk_shootr]

Wow,......all I thought I knew about springs has unraveled.

[Motivated1]

Great info Tom, thank you! Keep it coming.

[Clint]

Fantastic work! Could you define L1 and L2 please? What sort of service life were you getting out of these springs? Was there a gradual and predictable reduction in spring force or sudden drop off?

L1 is length 1, or the spring length (and associated force) while the action is locked in battery.

L2 is length 2 or the spring length (and associated force) while the action is bottomed out in full recoil.


A little background on the shock loading:

This phenomena is not uncommon in automatic weapons.

It is basically a wave that travels at high speed back and forth along the spring

The stranded wire spring ( as found in the Kalashnikov )
is specifically recommended for shock loading applications.

The friction between the strands helps damp the shock wave.


https://www.ctspring.com/press/2012/...d-wire-springs

http://www.smallarmsreview.com/displ...darticles=1967

https://www.roehrs-springs.com/sprin...i-wire-springs

[crosseyedshooter]

This topic is relevant to my interests. As a mental exercise to satisfy my own curiosity, I had measured a few springs to try and understand how spring parameters might translate into AR15 operation and perceived recoil. In concept, the spring stores the recoil energy and the reciprocating mass changes the harmonic frequency of the spring-mass system. In my case, I just wanted to look at the spring variable.

I used a digital trigger scale to roughly measure the force, in pounds, at bolt closed position and after (x) inches compression. I did this by installing the respective spring into a lower receiver with the corresponding buffer and measured the force needed to push the buffer away from the buffer detent horizontally. Then I used an extension of known length (x) to push the buffer and tried to get the force after (x) compression. I averaged three to five measurements each time. Those numbers are F1 and F@x. Due to the limits of the trigger scale, I had to calculate the bottom-out force of F2 at 3.5" of bolt travel.

I also measured other spring characteristics like coil count, free length, coil diameter, etc. and used spring formulas to back-calculate linear spring rate (k) and stored energy (1/2 kx^2). The below table is the data I've collected so far. I haven't had any time to do any analysis beyond a brief review of it and I'm sure there are many problems with it.

The flatwire springs with (Calc) in the description are calculated A5 extension values using measurements in a carbine extension as a sanity check to compare with actual A5 measurements. They seem to correlate for the most part.



There are some general observations I made from the data, although not precise due to the limits of my measurement system. I think there are valid general trends and physical principles.

• Flatwire springs have a higher F1 due to the longer free-length and more initial compression. The flatwire allows the longer spring to fit within the confines of the buffer and receiver extension at full compression.
• The A5 rifle spring follows a similar principle by using a longer free-length but instead, uses a longer extension to accommodate the longer coil spring.
• Even at the same spring rate, longer springs with more initial compression can store more energy within the same 3.5" of bolt travel. This will reduce the bottom-out impact and therefore, felt recoil until it prevents full bolt travel and proper function.
• Flatwire springs make a grinding sound and generally have more friction than coil springs in the same receiver extension.