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Author Topic: Stronger recoil spring for suppressed Tavor  (Read 2668 times)
ShootingSight
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« on: August 28, 2017, 07:12:14 PM »

There are two threads going, one called 'Any machinists here', and the other titled 'Hey IWI'.  Both discuss a stronger recoil spring for the Tavor, so when you shoot it suppressed the recoil is not so violent.

So I pulled my Tavor apart and measured the OEM factory spring, then ran spring calculations.
It is
0.050 wire
0.455 OD
19.125" free length
10" installed length
5.8" fully compressed length

I calculate the rate at 1.175lb/in
So it is under 10.7lb with the bolt closed, 15.6lb with the bolt open.

The guide rod is 0.343" diameter, what sucks is that the tube it fits in is 0.497" diameter.

I say 'sucks' because when I look at stock spring options, I found lots that are 1/2" OD, and of course the OD swells slightly as you compress it, so it would bind inside the piston tube.  This cuts down lots of options.

I ran calculations to see how we could stiffen it up, and looked at the total energy the spring would absorb.  I came up with options at +6%, +19%, and +25%, maybe a +32% (this might be a non-standard wire diameter), +40%, and +50%.  We are talking energy here, so the +50% means bolt closed force would be about the same as the bolt-open force is today.

Bad news is that with the limit on the OD I was not able to find stock springs.  I'll keep looking, but it looks like a custom spring run is $500 per option.

So the question is 'who is up for it'?  I'd propose we start with the +25% option.  We can always go down by cutting coils.  No going up without limiting bolt travel.

I'll throw $200 at the project, If we call the springs $50 each, I'd need 6 more people to sign up and buy one to make this a go.  Of course, if we guessed wrong, we are out the money.  Or if 10 people sign up at $30 ....  Happy to hear proposals.  I'd say 10 people at $30 would work, and then I'd keep the price at $50 if it does work.  That way the people who take the risk get a benefit.

Thoughts?
« Last Edit: August 29, 2017, 01:07:30 PM by ShootingSight » Logged

Art Neergaard
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« Reply #1 on: August 28, 2017, 07:32:53 PM »

I'm in, I'll specify the exact amount I'll pitch once we see how many people are willing to pitch in.

Thank you very much for your work regarding this subject, you found details that people like me would have no clue how to figure out.  Your work is appreciated.

Will this run of springs be one specific weight, or will we be able to try two different weights?
If trying only one weight for the first batch, I think the 25% would be a good place to start like you suggested.

Mods, we should sticky this thread.  I think once we figure out the right springs, a ton of more guys will want to buy Tavors to run cans on them.

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ShootingSight
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« Reply #2 on: August 28, 2017, 07:43:35 PM »

Unfortunately, the cost is per option.  The cost in springs is the machine setup.  For them, the actual cost per spring is small, but the base cost to set up and tune a machine is the bulk of the cost unless you are making thousands of springs.

I'd say let's let this thread run for a while and see the interest.  If it looks like enough, we can start a poll to collectively chose an option.  You might be on to something.  Enough people shoot the Tavor suppressed (especially now with the 300BLK option starting to ship) that there is a market out there.

I wonder if the 300BLK kit comes with a new recoil spring?
« Last Edit: August 28, 2017, 07:46:08 PM by ShootingSight » Logged

Art Neergaard
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« Reply #3 on: August 28, 2017, 07:58:23 PM »

Unfortunately, the cost is per option.  The cost in springs is the machine setup.  For them, the actual cost per spring is small, but the base cost to set up and tune a machine is the bulk of the cost unless you are making thousands of springs.

Makes sense.  So I assume you would be paying a third party to make the springs to the specs you ask?

Also, you mentioned earlier that if the spring weight is too heavy we could soften them by cutting a coil or two..  I'm sure we could get the first batch to work through trial and error pretty easily.  If 25% is too strong, maybe you or someone could calculate exactly how many coils softens the spring by what percent.
I like where this is going, I'm exited  Grin 
I've heard a few guys complain about cycling issues with a suppressor on their Tavor, so this could fix that.
Even though masking tape has cured any gas in face problems I've had, this would also help a ton.  Most gas I noticed leaks through the rear of the optics rail near the rear sight.

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« Reply #4 on: August 28, 2017, 08:00:21 PM »

I wonder if the 300BLK kit comes with a new recoil spring?

I wouldn't be surprised if it had a different spring weight, probably even softer than the 556 Tavor since it has an adjustable gas block for subsonic ammo.
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AZ-Chris
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« Reply #5 on: August 28, 2017, 08:40:04 PM »

Count me in on this.
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Hit Factor
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« Reply #6 on: August 28, 2017, 08:47:21 PM »

I'm in.
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l2a3
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« Reply #7 on: August 28, 2017, 11:35:14 PM »

Am I correct in believing that this "New" recoil spring will work in both the SAR & X-95 when suppressed?
Thanks for any reply.
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« Reply #8 on: August 29, 2017, 12:21:26 AM »

Am I correct in believing that this "New" recoil spring will work in both the SAR & X-95 when suppressed?
Thanks for any reply.

Yes, SAR and x95 use the same spring.

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ShootingSight
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« Reply #9 on: August 29, 2017, 08:22:11 AM »


Makes sense.  So I assume you would be paying a third party to make the springs to the specs you ask?

Also, you mentioned earlier that if the spring weight is too heavy we could soften them by cutting a coil or two..  I'm sure we could get the first batch to work through trial and error pretty easily.  If 25% is too strong, maybe you or someone could calculate exactly how many coils softens the spring by what percent.


Yes, I'm getting a spring company to make to my specs.  Spring winding equipment is very specialized, and not something a typical machine shop has.

Calculating coils to remove versus percent is the easy part, that is just math - I can take that spring and remove 1 coil, then 2 coils, then 3 coils, and tell you what percent reduction you get.  The trick is knowing what our goal is.  Nice thing is that if 25% is too high, and we go about this coil by coil reduction exercise, once we know what our target is for energy absorption, I can design the ideal spring based on that result.

It would cost another $500 run to do it, but by that time we would not only have the assurance that the idea has merit, but we would also know if enough people buy this to justify.  Personally, I think it has a chance.  Enough people shoot suppressed, and without a gas block valve, that there is a need.
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Art Neergaard
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« Reply #10 on: August 29, 2017, 08:55:05 AM »

BTW, the +25% energy option would make the charging handle go from 11lb load in the forward position and 16lb load in the back position, to 13lb in the forward position and 20 lb in the back position.
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Art Neergaard
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xdmikey
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« Reply #11 on: August 29, 2017, 09:38:36 AM »

I have never had any issues while shooting suppressed but I rarely put more than 100 rounds down range. Are the issues something that surface in excess of that total? Also, my usual cleaning routine would be swabbing the barrel for nothing I get clean patches. And I rarely shoot benched; at best I throw it over my bag.

This being said, I'd be in if I'm shooting on borrowed time so to speak.

Art, you'll be leaving this post open, looking for interest, right?

Thanks Art
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mikep7m10
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« Reply #12 on: August 29, 2017, 11:47:33 AM »

Would it be possible to nest a 'helper' spring?  At least as a trial to determine what weight is best.
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ShootingSight
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« Reply #13 on: August 29, 2017, 12:23:59 PM »

Unfortunately, there isn't enough space in the diameter to fit in an additional spring, nor is there any room in the length, as the current spring has the coils go solid (or very close) in the bolt back position.
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Art Neergaard
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« Reply #14 on: August 29, 2017, 01:11:51 PM »

I have never had any issues while shooting suppressed but I rarely put more than 100 rounds down range. Are the issues something that surface in excess of that total? Also, my usual cleaning routine would be swabbing the barrel for nothing I get clean patches. And I rarely shoot benched; at best I throw it over my bag.

This being said, I'd be in if I'm shooting on borrowed time so to speak.

Art, you'll be leaving this post open, looking for interest, right?

Thanks Art

Others need to comment on this. I've only shot my Tavor suppressed with a 30 cal can on it, which I assume produces less back-pressure than a 223 can, and I did not see any issues.  My involvement in this is because others suggested there was a need, and I did the spring math and know spring suppliers.
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« Reply #15 on: August 29, 2017, 05:52:14 PM »

It might take a little time to kick off once we find the correct spring ratio..
But I think in time there would be enough people wanting to buy aftermarket springs that it would be worth it.

I'm sure there are plenty of people reading this thread that don't post here waiting for the results.


Edit, eventually there would probably also be a market for the standard factory ratio spring that some might just want as an extra as well.  However I think the suppressor market is big enough that the extra power springs would dominate sales.
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« Reply #16 on: August 29, 2017, 06:24:13 PM »

I assume that if you want a spare standard power spring, IWI would be your best source.  They buy WAY more than I do, and will be able to offer the best price.

BTW, I looked up the 300BLK kit they sell, and it comes with a new 'recoil management system', so I presume they tuned the spring to make 300BLK work.
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Art Neergaard
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xdmikey
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« Reply #17 on: August 29, 2017, 07:36:21 PM »

Art, I have both 223 & 308 cans and I can shoot a vid showing gas/smoke. Unfortunately I will have to wait for the range in houston to dry out.
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Hkbeltfed
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« Reply #18 on: August 30, 2017, 06:29:37 AM »

I think you'll find stronger recoil springs will do little to nothing to keep the bolt closed longer or reduce gas. Search for George M. Chinn's firearms design books on the net for enlightenment.
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ShootingSight
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« Reply #19 on: August 30, 2017, 08:22:08 AM »

I think you are 100% correct.  If reduction of gas is the only goal here, the spring is not the answer.  A reduced flow valve would be the way to do that.

However my understanding was that when suppressed, the action cycles a lot more violently and there can then be issues with reliability.  So instead of the spring absorbing part of the energy, then the shooter absorbing the rest when the bolt carrier slams into the buttstock, a stiffer spring would mean more energy goes into the spring, so the BCG is moving slower when it reaches the end of its stroke.  This reduces the recoil shock to the shooter, and gives the trigger mechanism more time to catch the hammer sear reliably.
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Art Neergaard
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