My interest is specific to short barreled 9mm, but feedback from any configuration would be relevant.

I've searched high and low for flat wire buffer spring comparisons between the tried and true Tubb, and the copycat (?) Strike Industries offerings.  Lots of info on Tubb's spring, but virtually nothing out there about Strike's other than, "I like it" type stuff.  I've even emailed both of them (for different reasons, not necessarily comparisons) and not gotten a response.

First, let me be clear, I don't mind paying the extra $10 for Tubb's if it's better in any measurable way.  My main reason for being curious is there aren't many places to buy it, and I hate buying single items if I can bundle a few things and spread shipping around.  I know, that seems contradictory, being willing to spend more on an item but unwilling to spend more on shipping...

Strike's is carried lots of places, but none of them have any info as to spring strength.  Is it like Tubb's in that it's stronger with the bolt closed (10.5-13 lbs vs 9 lbs for regular springs) while being a similar ~16 lbs when open?  Strike only talks about the extra service life and shooting characteristics, but some youtube reviews mention it closing the bolt more firmly, so I assume it does have extra strength there (closed).

One buyer review at JBO mentions preferring the Tubb spring:

https://www.joeboboutfitters.com/Strike-Industries-AR-15-Carbine-Flat-Wire-Spring-p/si-ar-fws-c.htm

Could this be why Strike doesn't list spring weight??

Back to Tubb...  The commonly shared specs are 10.5 lb closed, 16.3 lb open for AR-15, and 13 lb closed, 16.7 lb open for AR-10/.308, but their website states 11.1 lb closed, 15.0 lb open for the latter (nothing listed for the former).  If that's correct, is there still any advantage to getting the longer .308 spring and trimming it to fit?  Did their AR-15 spring get lightened, as well, or is the only difference the extra 6 coils (36 vs 42)?

http://www.davidtubb.com/bufferspring-sr-ar10 - AR-10
http://www.davidtubb.com/tubb-springs/ar15-bufferspring - AR-15

I've never had an issue with any of the springs I have for ARs.

That said, I buy Tubbs for my light weight builds because they WEIGH so little.  I'd be interested to know what the strikes weigh.

That's good to know, thanks.  I was curious about actual weight, since the term is used interchangeably with strength.  With more air space between coils, but more length, I was hoping that lighter weight would be the case.

Tubbs LW spring comes in at 1.52 Oz. Strike is not listed currently...

Parts Weight Database:
https://docs.google.com/spreadsheets/d/1I6Qb6kAJjChEJ56qhznv2291c5UHRDyNXuSXGObumqM/edit#gid=2111764851

I suppose I should bookmark that google doc!  It's a lot more usable than the ever-growing thread.

My MAS Defense 9mm buffer kit's spring is 2 oz.  25% less for a flat wire is a nice bonus, you pay close to that per ounce just for weight reduction, regardless of performance gains.

^ Yeah, I put the Tubb spring on my wish list largely at your advice. :)

You use the .308 spring all the time, not the shorter AR-15 one?  Have you compared the open/closed specs you've posted before to the listing on Tubb's website?  I'm puzzled by the lower numbers now.

Are you sure you aren't David Tubb?  :)  I got an email from them 10 minutes before your reply, and that was after like 3-4 days of waiting!  I can't say their response inspires much confidence, clouding the issue and only partly addressing what I asked...

Sounds like a liability answer, not a functionality one.  To be fair, though, Strike Ind. hasn't replied to their set of questions yet.

http://www.defensereview.com/dr-follow-up-strike-industries-si-ar-carbine-flat-wire-spring-tech-details-best-tactical-ar-15m4m4a1-carbinesbr-short-barreled-rifle-actionbuffer-spring-ever/

I think ill buy one. Wish someone knew the weight.

Good find!  I've emailed Strike twice now, and called once, and haven't gotten a response with specs...

Those numbers look pretty low, though.  8/12 lbs is lighter than the commonly referenced standard A2 spring (8/15 or 9/16 lbs), and quite a bit less than Tubb's (10/16, 13/17, or 11/15 lbs).  It would be nice to know if their .308 flatwire gets up into the more normal "enhanced" range.  I suppose just matching M4 standard ain't bad...

The Tubb's lightweight spring is 7.5lb in battery and 14.2lb compressed. It's basically their standard flatwire with 6-7 coils clipped.

I use it in my 300BO and it allows last round bolt hold open with both supers and subs

That addresses one of the curious items with flatwire springs, whether the strength is simply a matter of the number of coils.  It may not be the full story, but it sounds like it's at least part of it.

LW = 7.5/14.2 lb, ~30 coils
Regular = 10.5/16.3 lb, 36 coils
.308 = 13/16.7 lb, 42 coils

Aside from your 14.2 lb open figure, the closed specs track pretty well by number of coils.  Of course, the newer 11.1/15.0 figures on Tubb's website for the .308 cloud the picture.

The LW specs are pretty close to Strike's.  If the actual item weight ends up being similar, that adds a good option for people not needing a high strength spring.

I had a few things in my Brownells cart to possibly order this week, since I need to get some Birchwood Casey Aluminum Black and they have as good of a price as any on the regular length Strike flatwire.  I just looked up something else and saw their regular special of free shipping on $50+ had been changed to $5 off $25+ and free shipping, good for another 2 hrs or so.  I couldn't pass up the flatwire spring and bottle of black stuff for $20, so I have Strike's regular length spring (.308 version not carried) on the way.  Should arrive in a week, per the checkout estimate.

My Strike Industries carbine flat wire spring arrived today.  Ironically, I finally got an email back from them this morning, apologizing for the delay (seasonal busyness) and saying they are looking into the specs I requested.  In the meantime, they recommend going with the .308 spring and cutting it to length as needed.  Doh.

Anyway, the carbine spring is 36 coils and weighs 1.6 oz on my nearest-0.2 scale.  That means the specs are probably very similar to the Tubb carbine length.

I couldn't believe how hard it was to get the spring over the buffer.  A regular piano wire spring slides over with no resistance.  The flat wire spring seemed too small at first, requiring quite a bit of coercion just to get it started, then having to be spun/wiggled up the length of the buffer, and finally, much prying to get it fully seated at the end.  I hadn't thought about it, but it makes sense it would be a tighter fit, since the O.D. can't be much more than the regular spring and still fit in the tube, so the extra width of the flat coils has to be on the I.D. side of the fence.

I didn't have any easy way to test spring strength by hand, but with it installed and the bolt held back by the bolt catch, hitting the paddle and letting it fly resulted in a pretty viscous closing of the bolt.  It's definitely stronger than the regular spring in the extended position.  The compressed position feels mildly stronger, requiring a little more effort to pull back on the charging handle, but nothing extreme.

Yeah, I was thinking of doing a simple test like the balsa wood bridges of our youth, seeing how much weight I could stack on each spring.  They were too tipsy to go far with that idea, however.  They need something like your pipe suggestion to contain the travel.

If I had to make a mostly uneducated guess, I would say Strike Ind. reverse engineered Tubb's spring to end up with something very similar, and that's why they don't have the specs readily available.

David said the 42 coil can be tuned. Every 3.6 coils cut equal 1# of weight. There is a better video of him testing on YouTube.

That sounds about right from what I outlined a couple posts up.  Every 6 coils looks like 2-3 lbs.  Seems like the different springs are identical other than their length.  A longer spring compressed into the same space has more effective strength over that confined travel.

I've used an unused buffer tube and a second buffer and a digital scale.

Basically set a buffer (or dowel rod) on the scale to use as a spacer and zero out the scale.
Take the spring, buffer, and tube and hold it upside down over the scale and while holding the buffer (or dowel spacer) to the buffer installed in the spring, press down until the front surface of the buffer is even or just inside the end of the tube.
The reading on the scale is the bolt closed spring weight.

Press down roughly 3" or until the edge of the tube is just short of touching the scale surface. This reading would be the spring rate with the bolt back.

You could actually use the bolt carrier group standing on end as the spacer, just make sure to zero/tare the scale out with it on the scale so doesn't add the weight to your reading.

I used this method when cutting the standard Tubb's spring to make a lightweight spring. I had one of each and found that both my pistols liked the lightweight spring better (with lightweight BCG and adjustable gas block). I contacted David Tubb and he said I could cut up to 7 coils off the standard spring to make it a lightweight spring instead of buying a new spring. I did the above method with my lightweight spring to get the baseline readings, then cut a coil off standard spring and took a reading, then cut another, etc until I had the weight I wanted

The approach makes sense, but I'm not quite following your methodology.  You've got a zeroed buffer facing up on the scale, then a spring/buffer/tube facing down on top of it, correct?  Which buffer is being referred to in the bolded part?  I'm thinking it has to be the zeroed one, as the top one is already inside the tube.

Also, the length of the buffers and tube would have some affect.  Are we talking two 9mm buffers and pistol tube, one 9mm buffer and one carbine buffer and a pistol tube, one 9mm buffer and one carbine buffer and a carbine tube, two carbine buffers and a carbine tube...  I'm guessing the latter, which of course I have none of to test with.  :)

Did you come up with that approach by measuring the bolt's length of travel relative to 2x buffer length?

Yes, just imagine the setup being on the pistol/rifle and the way it cycles.

The second buffer is being used just as a spacer to help push on the spring/buffer assembly. Anything can be used that's 1" diameter or less. A wood dowel, the BCG standing upright on the bolt face, etc.

Got it, but how are you ensuring that the compression range you're measuring at is the same (or close enough) as the spring length when the bolt is closed?

FWIW, Spinta just introduced their flat wire spring this week.

http://www.spintaprecision.com/ar-15-and-ar-9-flat-wire-carbine-spring-christmas/

I count 35 coils instead of the usual 36.  Other than that, all I can add is, it's priced competitively.

I used to play around with Tubb flatwires and various Sprinco weights until I discovered the Armaspec Stealth Recoil Spring. It makes life so much easier.

Armaspec SRS

That's nice, but not particularly relevant. ;)  It may be a superior system functionally, for all I know, but it [presumably] doesn't offer the linear strength and increased duty cycle of flat wire, so the comparison doesn't do much for us.

picked up a spinta flat wire its 14 5/8 long with 36 coils the strike industries  is 13 7/8 long with 35 coils if any body still cares

That's weird.  My Strike Ind. spring is 36 coils and I counted 35 coils in the Spinta picture.  I didn't measure the uncompressed length of the Strike spring.

Have you fired both to form a comparison opinion?

not yet but just working the charging handle I cant tell the difference between the two.

I just got a Strike Industries Flatwire spring to use in my newest build.  They were on sale at Brownells with free shipping, otherwise I would've gone with a Tubb's like in my other builds.

I tested this one like I described above and it measured 7lbs bolt closed in battery and 12lbs at bolt hold open (give or take a couple oz).  Much like the lightweight Tubb's spring, but less than the standard Tubb's spring (which is supposed to be an extra power spring anyway).

I haven't gotten to the range yet to test (It's been way too cold here).  This is on a mid-length gas build with a standard weight auto bolt carrier.  I do have a couple different weight buffers to try, 3oz, H1, H2.

I do run the Tubb's lightweight springs on 2 lightweight builds. One is 300BO, the other 5.56.  Both have adjustable gas blocks, lightweight carriers, and Taccom lightweight buffers.

EDIT: I made a typo with the weight, it was 12lbs compressed, not 10

Also, noticed when hand cycling the bolt, it seems the SI spring is a bit noisier than the Tubb's spring

Thanks for the report.  That's in fairly close agreement with the 7.7/12 lb specs JerDerv found.  But, you had mentioned previously the Tubbs LW spring being 7.5/14.2 lbs, so it sounds like your testing method is working consistently for bolt closed (uncompressed) but has a pretty big margin of error for bolt open (compressed).

It's looking like Tubbs' manufacturing process produces a higher quality product, with their LW spring being comparable to SI's but at significantly lighter weight, while their regular spring is extra strength at the same weight.  Durability claims are similar for both, so there's no apparent penalty to the lighter weight.

I made a typo when I posted the spring weights.  It should've been 12lbs compressed instead of the 10lbs I posted.

Gotcha, that changes things.  That confirms it being standard strength at bolt open and mildly stronger at bolt closed, being a good replacement for regular springs if you want better duty cycle and lighter weight.

I also see your addition about the Strike spring being noisier.  Mine was pretty raspy initially, too, but smoothed out quite a bit after a week or so of hand cycling.  I attributed that to the new buffer tube about the same time, but it may well be the tolerances of the Strike spring being tighter in the tube.  You didn't by any chance put some calipers on the Strike and Tubbs springs to see if Strike's coils are ever so slightly wider?