9mm Evanix Blizzard / Rainstorm tuning

[wwonka]

Barrel length is 55cm = 21.7" and then some 2" of empty shroud after the barrel. I'll take some photos when I put the gun back together, now that it still looks like a traditional gun

Come to think of it, is there actually any difference in between the Blizzard and the Rainstorm? They seem to have the same action, shroud, stock - some changes in the stock checkering perhaps? Same gun with different names for different markets?

I think that the Rainstorm .357 have pretty much the same specs as the Blizzard .357 - exact same barrel length etc.  The shot strings are similar as well, which leads me to believe that the valves and ports are exactly the same (but I could be wrong on that since I have not compared).

In the .22 caliber, the .22 Blizzard has the longer 21.7" barrel, while the .22 Rainstorm II has the 19" barrel.

[Nomadic Pirate]

My Blizzard has a longer air tube and a much beefier reciver

[rkr]

The PEEK rod arrived today so I turned a new seal for my original valve and put the mechanism together. After putting in pressure the valve was hissing a bit so I took some empty shots to slam the valve a bit and it quieted down. I'll leave the gun for a pressure test until tomorrow. If the valve holds it's time for new o-rings and some testing. I still think I'll get/make/have made a spare valve without the o-ring groove in the stem.

[dogwood]

The PEEK rod arrived today so I turned a new seal for my original valve and put the mechanism together. After putting in pressure the valve was hissing a bit so I took some empty shots to slam the valve a bit and it quieted down. I'll leave the gun for a pressure test until tomorrow. If the valve holds it's time for new o-rings and some testing. I still think I'll get/make/have made a spare valve without the o-ring groove in the stem.

Keeping my eye on this, might have to go the same route, looking forward to hearing how it works out.

[rkr]

First test with the PEEK then.

This is a comparison string, shot with stock seal that's turned upside down. The lip of the seal forms a sharp edge at roughly 1mm above the cup of the valve:

200 bar, 6,1 gr bullets +4 turns
794 - 132 fpe
810
804
812
830 - 160 bar - 144 fpe
826
821
811
778
765 - 130 bar - 122 fpe

Then PEEK seal. The seal is 1mm longer than stock and it comes 2mm out of the cup and also has that sharp lip.

200 bar, 6.1g, 0 turn

651 fps
664
671
674
685

The power is very low at 100 fpe and there's clearly too little spring force in play. I'm low on bullets so I'll increase the tension:

200 bar, 6,1g, +4 turns

716 fps
732
742
751
765

Still too little spring and the power is at 122 fpe. I'll turn the spring tension to max:

200 bar, 6.1g, 6 turns (sear won't lock at 7 turns)
745
758
783
795
812 - 138 fpe
---- 160 bar
812
768
738
---- 150 bar (only 10 bar for 3 shots? perhaps the previous was 170 bar after all) and I'm out of bullets.

Now the interesting thing is that I can't get enough hammer power to the valve now. The valve is 1mm longer with thicker seal so it has more mass and some more spring tension behind it. Could that be the whole reason for my low power or does it have more to do with the PEEK material? How much would I gain by smoothing out the seal edges and perhaps shortening it to stock length? I guess these question must be answered.

Right now I'll continue the pressure test to see if the additional pounding of the valve helped sealing it.

Oh, worth noting is that I was still using those badly worn o-rings in the valve housing. That may be part of the problem, new o-rings for the next round is the seal holds. If it won't then I think I'll be trying some ertalyte as my next seal material.

[rkr]

Some photos as requested before I tear the gun down. I was hoping for some sunshine but this time you'll have to do with these photos taken in a blizzard 

[rkr]

I made a new PEEK seal and the gun is doing it's deeds again.

A 7 shot string from 200 bar fill with 88 grain bullets:

--200 bar
864 fps
868 fps (147 fpe)
861 fps
861 fps
864 fps
--155 bar
853 fps
835 fps
--140 bar

Heavier bullets would have given more FPE but I don't have any at my disposal. I'll have to see if the gun will hold air now and if it does I have some additional mods planned I could try.

[Sfttailrdr46]

  Very nice now , now we just need to survive until 50+ degree weather so all this white stuff goes away and we can all get back into full swing

[wwonka]

Looks like you're back on track. So... the net change was that you replaced the original valve stem with a PEEK rod, and made a new seal for the original valve?

[rkr]

Looks like you're back on track. So... the net change was that you replaced the original valve stem with a PEEK rod, and made a new seal for the original valve?

I also opened up the shaft tunnel to 8mm diameter. It seems that I'm now facing another bottleneck that limits the power to 150 fpe. I have a strong guess what it is so we'll see if I can fix it. As you can see the string for the first five shots is rather flat and the power drops off quickly after that. Based on that, can you give me an educated guess where the limitation is?

[wwonka]

Good question, I am not sure. I compare it to an earlier string you had (below) with a longer bell curve - but that was at 79 grain pellets at 133 FPE peak, and not 147 FPE with 88 grain as was your latest.  As an engineer I would begin with an apples-to-apples attempt, and maybe try a string with the 79 grain pellets again to see a side-by-side comparison with what you got before the PEEK rod.

200 bar with JSBs
822 fps (first shot after tune, I guess it's OK to be low)
860 fps
870 fps
865 fps
862 fps
866 fps
866 fps
840 fps
827 fps
816 fps
130 bar

EDIT: On the face of it, It does look like an air-usage/efficiency opportunity. Once you've got an apples-to-apples comparison, it might be easier to plan where to go next - but one thing that might have an effect is hammer spring tension (or pre-load). Check out this thread, particularly what rsterne had to say about shot strings, spring-tension effect and efficiency/air usage.

http://www.gatewaytoairguns.org/GTA/index.php?topic=61382.msg588530;topicseen#new

... That's just one idea. Lot of pellet usage for all this testing, that's for sure. Shoot me a PM if I can contribute to the experimentation by sending you some pellets or whatever.

[rkr]

No, it's not as simple as hammer spring tension. What I suspect is this http://www.gatewaytoairguns.org/GTA/index.php?topic=59414.0

The valve housing is quite small and is in practice a chamber pot. The inlet hole is only 7.5mm so ...

[rkr]

As usual I was right  I opened up the valve inlet to 9mm and took off the valve spring, no other changes. This is the result:

200 bar, 88 grain bullets
904 fps - 160 fpe
904 fps
897 fps
880 fps
861 fps - 150 bar
836 fps
817 fps
804 fps - 125 bar

So, now I have a bit too much spring in it and the flow limit is most likely in the transfer port (as it should). Opening up the TP to 7mm might net me another 10-20 fpe but I don't know if I really need that. I think I'll be studying the hammer bounce next and see if I can eliminate that. What's interesting in this shot string is that it doesn't drop as fast as it used to, so improving the flow in to valve housing has given me more potential at lower psi. If I turn down the hammerspring I should be getting nice and long strings with JSBs for long range target shooting.

[rkr]

Eliminating the hammer bounce:



Second soundtrack is muzzle burst with stock spring and 6 turns in, you see 6 valve openings.

Fourth track is muzzle burst with stiffer spring that doesn't push the hammer agianst the valve, you see two valve openings.

The downsize is that power dropped 25 fpe. Back to the drawing board.

[wwonka]

Just thought I'd be the first to say: looks like you were right.

It seems that the closer you get to a consistent unrestricted bore throughout the airflow (valve, transfer ports, etc) matching the 9mm diameter of the bullet, the better. Which makes a lot of sense.

I am still wondering (for an apples-to-apples comparison) what a 10-shot string with the JSB 79 grain pellet would look like at these tune settings that gave you that last impressive string (the one peaking at 160 FPE with the 88 grain bulllet).  Maybe with the spring pre-load backed off a little, for that bell curve again.

It should be possible to calculate this -  but do you think the bullet is out of the barrel before those second and third hammer strikes that are showing on your soundtracks?

[QVTom]

Eliminating the hammer bounce:



Second soundtrack is muzzle burst with stock spring and 6 turns in, you see 6 valve openings.

Fourth track is muzzle burst with stiffer spring that doesn't push the hammer agianst the valve, you see two valve openings.

The downsize is that power dropped 25 fpe. Back to the drawing board.

Where in the shot string is the worst bounce occurring?  In my stock RS2 22 cal stat to get audible bounce at shot #18 which occurs ~2000 psi.  My gun will sound like a trumpet and produce wild deviations if I shoot 14gn ammo with the factory tune.  I know there is no reason to shoot light and loose ammo with a factory tune but I think the bullet weight and back pressure play a large roll in regards to bounce in these guns.  I just don't understand the why.

Tom

[wwonka]

It should be possible to calculate this -  but do you think the bullet is out of the barrel before those second and third hammer strikes that are showing on your soundtracks?

... Answer to my own question: unless you have a 12 foot barrel, the answer is yes.

[rkr]

Eliminating the hammer bounce:


Second soundtrack is muzzle burst with stock spring and 6 turns in, you see 6 valve openings.

Fourth track is muzzle burst with stiffer spring that doesn't push the hammer agianst the valve, you see two valve openings.

The downsize is that power dropped 25 fpe. Back to the drawing board.

Where in the shot string is the worst bounce occurring?  In my stock RS2 22 cal stat to get audible bounce at shot #18 which occurs ~2000 psi.  My gun will sound like a trumpet and produce wild deviations if I shoot 14gn ammo with the factory tune.  I know there is no reason to shoot light and loose ammo with a factory tune but I think the bullet weight and back pressure play a large roll in regards to bounce in these guns.  I just don't understand the why.

Tom

The worst bounce occurs in low pressure as there's not enough backpressure in the valve to prevent it from opening. Heavier bullet may slow down the valve closing (as the valve starts closing while the bullet is still in the barrel) causing less strike to the hammer and less bounce.

Let's take a look at this soundtrack with a gun that makes a bit less noise and actually shows the action soundtrack (the lower tracks with bounce that is):



1ms the trigger is pulled and hammer released
6ms the hammer hits the firing valve causing air burst
7ms air and or pellet is moving in the barrel
9ms air is bursting out of barrel, pellet has left
10ms valve has bounced back and hits the hammer
17-18ms hammer hits the valve for a second time and the cycle is repeated
28ms third hammer strike that's not strong enough to open the valve

So, as we can see there's only 1ms difference in pellet leaving the barrel and valve hitting the hammer. With heavier bullets it is entirely possible that the pellet in the barrel indeed slows down the hammer closing enough to reduce the bounce.

[rkr]

The PEEK seal leaks without the additional pressure of the valve spring so I will put the spring back in. To prevent it from blocking the flow I made this valve spring holder piece:

[Sfttailrdr46]

  I'm not an engineer but for better air flow shouldn't the leading and trailing edges be rounded or tapered where they are in the air stream for less turbulence of the flow ?