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Gas efficiency issues, anyideas team?

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Any advice on gas efficiency?

 

I’ve done everything I can think of or have been advised to do to make my Tavor useable, no dice so far. 


This lot didn’t work:

 

Cooled mags, filled, warmed
Replaced fill valves with known good ones
Properly lubed all internals, bolt is free running.
Rebuilt nozzle and opened up exit hole to ease pressure on system.
Replaced feedlips with Unifeeds
Shimmed gas routers

The only way the gun runs useably is on HPA

I’m open to any and all advice 🤷🏼‍♂️

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Can you expand on the efficiency a little my friend. :)

 

Is it wasting a lot on each shot? Is it not completely firing a full mag off to empty before gas depletion? Or something else?

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9 minutes ago, Immortal said:

Can you expand on the efficiency a little my friend. :)

 

Is it wasting a lot on each shot? Is it not completely firing a full mag off to empty before gas depletion? Or something else?

 

First 12 or so shots, exactly as expected, then less and less power  up to 19th bb, then mag degasses remainder (only a very small amount), then nothing.

Not obviously wasting gas until about the 15th bb

 

Typically, KWA gas M4 mags fills last around 60bb’s, or one and a half mags

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Would it not be worth reverting each mod back to stock bit by bit to see if things improve? So you can isolate the cause?

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Have you looked at the trigger group? Perhaps the mags are being emptied quicker because the hammer is keeping the valve open for too long?

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15 minutes ago, Cipher-032 said:

Would it not be worth reverting each mod back to stock bit by bit to see if things improve? So you can isolate the cause?

 

Problems before any mods, so no, that will make no difference, but thanks anyway

 

12 minutes ago, UKCYukarin said:

Have you looked at the trigger group? Perhaps the mags are being emptied quicker because the hammer is keeping the valve open for too long?

 

It’s a possibility, thank you

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I’ll resist the urge to give my usual sarcastic KWA answer as it’s you 😂

 

When you manually cycle the bolt, does the nozzle stick inside the bucking like it should until the bolt is to the half way point(ish) before springing back? Could be loosing gas there.

 

the float valve spring could be too stiff and it’s not allowing the float valve to do its job properly.

 

Do you have a kwa npas? Might be worth trying that and seeing how the adjustment effects the gas efficiency. I had a similar issue with that shitty mega arms. 

 

Piston compression. Does it have an o ring or one of those crappy piston skirt things? That’s usually an area of improvement of WE GBBR’s. 

 

Valve knocker issue. Perhaps it’s letting too much gas out of the mag or not returning to the rest position quick enough. 

 

Failing that, I’d say something is off spec like the BCG cylinder has been machined wrong. 

 

You’ve got 3 seal areas. Hop bucking, nozzle seal and mag to nozzle mating. If it’s neither of those things it has to be at the point the gas is entered into the system or a float valve issue. Have you tried other mags?

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replaced hammer or recoil spring?

 

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16 minutes ago, Wo1f said:

I’ll resist the urge to give my usual sarcastic KWA answer as it’s you 😂

 

Bwahahahaha

 

16 minutes ago, Wo1f said:

When you manually cycle the bolt, does the nozzle stick inside the bucking like it should until the bolt is to the half way point(ish) before springing back? Could be loosing gas there

 

Unfortunately not, works exactly as it should (now I stripped, cleaned and rebuilt the bolt lol

 



16 minutes ago, Wo1f said:

the float valve spring could be too stiff and it’s not allowing the float valve to do its job properly.

 

Good shout 👍🏻

 

16 minutes ago, Wo1f said:

Do you have a kwa npas? Might be worth trying that and seeing how the adjustment effects the gas efficiency. I had a similar issue with that shitty mega arms.

 

I don’t, that’s the reason I enlarged the exit hole though, I’ll get one 

 

16 minutes ago, Wo1f said:

Piston compression. Does it have an o ring or one of those crappy piston skirt things? That’s usually an area of improvement of WE GBBR’s. 

 

O-Ring, and a good fit, much better than the the crappy Vector skirt

 

16 minutes ago, Wo1f said:

Valve knocker issue. Perhaps it’s letting too much gas out of the mag or not returning to the rest position quick enough. 

 

Another likely culprit, I’m tying to order a complete new set of springs at the moment👍🏻

 

16 minutes ago, Wo1f said:

Failing that, I’d say something is off spec like the BCG cylinder has been machined wrong. 

 

You’ve got 3 seal areas. Hop bucking, nozzle seal and mag to nozzle mating. If it’s neither of those things it has to be at the point the gas is entered into the system or a float valve issue. Have you tried other mags?

 

Sorry, BCG.

 

I’ve PTF’d the hop rubber where it attaches to the barrel, does t seem to be obviously blowing at the seal, and I thought mag to nozzle, but my (rather hasty) first attempt at shimming the gas router made no difference. Any experience on materials and thickness you. An suggest?

 

Float valve seems likely as well, I have 8 mags, all do exactly the same, which makes me think it’s the rifle.

 

 

Cheers @Wo1f really appreciate your time, given me some more avenues👍🏻

 

 

 

10 minutes ago, heroshark said:

replaced hammer or recoil spring?

 

 

Recoil spring is massive, not easy to replace, and seems OK, I’ll be trying to get hold of a complete new spring set, cheers 👍🏻

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I’ve got a system 7 NPAS. PM me your address and I’ll send it to you.

image.thumb.jpg.de9d1c2091f59feb9a72181dae17ad21.jpg

 

ive shimmed a scar H mag before using that soft plastic stuff that holds 4 cans of Guinness together. Seemed to work quite well 😂

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6 minutes ago, Wo1f said:

I’ve got a system 7 NPAS. PM me your address and I’ll send it to you.

image.thumb.jpg.de9d1c2091f59feb9a72181dae17ad21.jpg

 

ive shimmed a scar H mag before using that soft plastic stuff that holds 4 cans of Guinness together. Seemed to work quite well 😂

 

You are a star, thank you, PM incoming mate 👍🏻

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Maybe worth seeing if it'll run with lighter hammer /recoil set to ease the cycle.

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42 minutes ago, heroshark said:

Maybe worth seeing if it'll run with lighter hammer /recoil set to ease the cycle.

 

Unfortunately, there are zero alternatives on the market at the moment, but a good thought, thanks

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Just now, rocketdogbert said:

 

Unfortunately, there are zero alternatives on the market at the moment, but a good thought, thanks

This may not be useful as it may work differently ,but. I've tweaked recoil springs on pistols before by cropping the spring to the length of travel then if the spring is not enough I add shims on the guide rod to increase the compression of the spring . You can do the same on a straight hammer spring but you can also bend lever springs to reduce tension if you are careful.

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5 minutes ago, heroshark said:

This may not be useful as it may work differently ,but. I've tweaked recoil springs on pistols before by cropping the spring to the length of travel then if the spring is not enough I add shims on the guide rod to increase the compression of the spring . You can do the same on a straight hammer spring but you can also bend lever springs to reduce tension if you are careful.

 

I got a response from Esti at  kscpart.com last night, no factory parts will be available  until May at the earliest, so I think you’re on the right track.

Ill try the NPAS, and see what can be done about the trigger spring👍🏻

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I think the KWA's are built without the use in cold climate in mind as their primary markets are warmer places than our cold little island. 

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1 minute ago, heroshark said:

I think the KWA's are built without the use in cold climate in mind as their primary markets are warmer places than our cold little island. 

 

You could be correct, but I have been firing it indoors so it shouldn’t matter lol

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eeesh that bad eh

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Well... I did warn you ;)

 

I really hope you get this working though! It'll be stunning when finished. If you have FB make sure to join up to the KWA gas group. 

 

https://www.facebook.com/groups/430462560486468/?ref=br_rs

 

There's a fair bit in there with people mucking around with the Tavor. 

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9 minutes ago, Asomodai said:

Well... I did warn you ;)

 

I really hope you get this working though! It'll be stunning when finished. If you have FB make sure to join up to the KWA gas group. 

 

https://www.facebook.com/groups/430462560486468/?ref=br_rs

 

There's a fair bit in there with people mucking around with the Tavor. 

 

Ha ha yep, works so well on HPA it will eventually work well on gg lol

 

Cheers for the link btw 👍🏻

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Well Rockdogbert I fell asleep and I see a load if adice has been given already lol :lol:

 

My grey matter thinks springs will be the answer to control the amount of gas used or perhaps wasted as it were. From watching videos of the Tavor they seem to pump loads of gas out the shell ejector port on the blowback, far more than appears to serve any purpose. The NPAS would control limiting the gas expelled down the barrel but in terms of wasting gas; stronger springs on the valves would reset the valve to closed quicker letting less out in the first place - or a weaker spring on the bolt carrier to strike the valve softer but I'd opt for a stronger closing spring rather than the weaker opening option. 

 

Curious if you've tried Red Gas and if you get the same issue. Some of the vids show the Tavor with some high FPS numbers (higher than UK legal) so I wonder if the FPS limit we have here is causing a lack of performance in how the parts are gelling together. Just thinking if it was designed to run on a more powerful setup and it's been in turn handicapped for our market resulting in poor performance etc... not sure if that makes any sense - I can try and reword it. :lol:

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You’ve got a set amount of gas leaving the magazine (assuming the valve knocker is functioning properly).  

 

How that gas is distributed between pushing the BB and powering the blowback is down to the float valve. I think using a softer and or shorter float valve spring will help. I’d also try a mag of .20’s and a mag of the heaviest BB’s you can find and see if that makes a difference as the float valve works on pressur difference. The heavier the BB, the longer it’s in the barrel being pushed by the gas (hence joule creep on GBBR’s)

 

 

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38 minutes ago, Immortal said:

Well Rockdogbert I fell asleep and I see a load if adice has been given already lol :lol:

 

My grey matter thinks springs will be the answer to control the amount of gas used or perhaps wasted as it were. From watching videos of the Tavor they seem to pump loads of gas out the shell ejector port on the blowback, far more than appears to serve any purpose. The NPAS would control limiting the gas expelled down the barrel but in terms of wasting gas; stronger springs on the valves would reset the valve to closed quicker letting less out in the first place - or a weaker spring on the bolt carrier to strike the valve softer but I'd opt for a stronger closing spring rather than the weaker opening option. 

 

Curious if you've tried Red Gas and if you get the same issue. Some of the vids show the Tavor with some high FPS numbers (higher than UK legal) so I wonder if the FPS limit we have here is causing a lack of performance in how the parts are gelling together. Just thinking if it was designed to run on a more powerful setup and it's been in turn handicapped for our market resulting in poor performance etc... not sure if that makes any sense - I can try and reword it. :lol:

 

When this was mine I tried Red gas and didn't make any difference, that and it was running about 360+ FPS

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4 minutes ago, Asomodai said:

 

When this was mine I tried Red gas and didn't make any difference, that and it was running about 360+ FPS

 

Cool, well that saves some gas and time... :)

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Well guys, @Wo1f is a certified genius.

Just fitting the NPAS, without adjusting it, I now get 38rounds a mag, and no out venting of gas.

 

I prostrate myself to you, sir, god of gbb 😊👍🏻😊

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