Air Gun Home :: View topic - New Old Project - Hayabusa PCP

yourdaddyjoe · Supporting Member

Oh come on Bob... Just funning ya...

That thing is going to be "The Beast"!

domer_pyle · Senior Member

You guys with your awesome machinery and shop skills make me green with envy

rsterne · Moderator

Right back at'cha' Joe.... Mr. Green

I'm sure looking forward to getting the first shots across the Chrony....

Bob

rsterne · Moderator

I got the gun assembled to the point of some tethered test firing today.... but I've still got some work to do.... I did some 2000 psi fills of the main tube and then shot some strings.... The velocity at 2000 psi was down quite a bit from expectations, but I did manage to record a string of 16 shots starting at 1900 psi and ending at 1000 that averaged 947 fps with 18.1 gr. JSB Heavies (36.1 FPE).... It started at 908 fps, peaked at 980 (at only 1400 psi!), and ended at 901.... The total energy was 577 FPE from a 62 Bar drop on the 115 cc main tube (7.0 CI).... Total air used was 434 CI for an efficiency of 1.33 FPE/CI.... That's significantly better than I have ever had at those power levels.... and more power than I have ever seen at 1400 psi as well.... My Disco and regulated 2260 PCPs run about 1.04 FPE/CI at 36 FPE....

I was having trouble cocking the gun, the hammer is a bit too long and barely latches when I pull the bolt all the way back.... After maybe 50 shots, the gun would no longer cock at all, and on disassembly I found the trigger sear was broken in half.... There was a mark on the hammer where it looked like the middle shoulder was impacting the sear and broke it.... That impact was likely stopping or retarding the hammer and preventing it from opening the valve fully.... When I made the hammer, I basically made a larger version of the 22XX hammer.... but the trigger assembly is from a Marauder.... I didn't have a drawing of the MRod hammer when I made mine but now I find out that it is quite different.... It is a cylinder with the sides milled off to reduce the weight.... but the bottom that rides over the sear is smooth.... The "waist" I machined into my hammer was apparently hitting the sear hard enough to shatter it.... I've got Joe at MuzzleMack getting me a couple straight from Crosman because MRod parts in Canada are nearly impossible to get (sorry, Eric!)....

So the first tests are both disappointing and encouraging at the same time.... I was expecting great things from the heavier hammer in regards to opening the valve at higher pressures.... So far, that hasn't happened, but if the hammer was indeed hitting the sear as it appears, then the tests were flawed.... On the other hand, I'm already at 36 FPE with 18 gr. pellets at only 1400 psi, with better efficiency than I have ever seen before.... Mr. Green

Things are now on hold until I can get a new sear and make a new hammer.... Rolling Eyes

Bob

rsterne · Moderator

Well guys, i seriously need some help with this gun.... Embarassed

I made a new hammer that is cylindrical (no notch) and installed the new sear and the hammer no longer strikes the sear on firing.... However, I'm still nowhere near what I was hoping for the power potential of this gun, and I've created another problem.... Not only is the hammer strike nowhere near what it needs to be to dump 2000 psi, let alone more.... but I'm getting hammer bounce at 1700 psi.... and at 1500 psi it bounces enough to completely empty the reservoir.... Shocked

Here are the practical differences between the Hayabusa and my modded Disco, as far as the valve and hammer are concerned....

1. The valve porting is larger, and the valve throat is 1/4" instead of 7/32".... but it still uses a Disco poppet....
2. The hammer is larger in diameter and heavier, about 100 gr. instead of 60 gr....
3. The hammer spring is the same, set just shy of coil bind....
4. I have an adjustable fall distance on the hammer but it's set for about the same fall as the Disco....

The gun is currently shooting about 700 fps at 2000 psi, and about 850-900 fps at 1500 psi (when it dumps all the air).... With the previous hammer (95 gr. with notch that shattered the sear) I got the following string (18 gr.pellets) from 1900 psi down to 1000:

908
921
933
941
962
966
971
976
977
980
973
966
944
926
913
901

By comparison, with my Disco when maxed out.... I was able to drive the same pellets at 1080 fps at 2400 psi.... I know from past experience that a heavier hammer tends to dump more air and allow higher pressures to be used.... So WTF is going on here?.... Is it possible I have way too much hammer weight and the spring can't accelerate it enough?.... Why is the hammer bouncing?.... and WTF do I try next?.... HELP !!!....

Bob

yourdaddyjoe · Supporting Member

The only time I got massive hammer bounce is when I made my transfer ports too big...

rsterne · Moderator

hmmmmmmmmm.... I got bounce on my 9mm with large ports as well....

Have to ponder that....

Bob

oddtodd · Silver Status Member

Could it be an air cushion event that is causing the bounce? The air acting as a spring to make the valve bounce? I watched on a TV show how they used an air cushion to create a shock wave in a jet engine to make it burn more efficiently at a certain RPM range. Could that air escaping at 1500 PSI be causing the same type of thing? You could have hit just the wrong spot by opening up the valve body? Just a thought.

Gippeto · Member

You built a machine gun too eh Bob? Laughing

On my scratch built "Disco", the issue ended up being bleed by from the valve stem...bored the rear of the valve body and fitted an o-ring. Wouldn't have believed that much air could get past the valve stem.

Also drilled "that hole" that's in the 2240 tube...the one that doesn't seem to do anything....it seems it DOES do something...it bleeds off the gas leaking past the valve stem in addition to relieving compression in front of the striker. Wink

Those two changes took care of the daka-daka in my case.

Could be the notch in the old striker was acting the part of the vent hole?

Al

rsterne · Moderator

VERY good thoughts, Al.... Maybe that's why the MRod striker has two flats machined on the sides, to allow blowby.... I thought it was just to lighten it.... BTW, my valve stem fit is less than stellar, so that could easily be part of the problem....

Bob

rsterne · Moderator

Thanks to Al (Gippeto), all it took was one freakin' hole drilled between the hammer and the valve to cure this thing.... Mr. Green

I drilled a 3/16" hole in the side of the tube with the back edge of the hole level with the end of the valve stem.... and VOILA!.... no more problems with runaway hammer bounce.... OBVIOUSLY (now!) there was an air cushion forming between the hammer and the valve, more than likely made worse by a less than stellar fit for the valve stem that was leaking high pressure air during the shot cycle.... This was not only slowing down the hammer and producing the velocity loss.... but causing the hammer to bounce as well.... The previous hammer wasn't as good a fit, and was likely leaking air around the perimeter so didn't exhibit this problem.... This is a case where a poorer fit actually worked better (by masking a potential problem).... Shocked

The Hayabusa is finally beginning to show its potential.... I fitted a 0.042" wire hammer spring that is only slightly stiffer than the one I had in my Disco and immediately achieved over 50 FPE.... The valve will now open properly at 2000 psi, and while I can hear a bit of hammer bounce at below 1500 psi, there is no "machine-gun Kelly" action taking place even at 1000 psi.... Since this gun will be regulated at 2000 psi eventually, hammer bounce is no longer an issue.... Here is the first decent shot string from this gun, using JSB 18.1 gr. Exact Heavy pellets....

2200 psi fill
1029
1055
1068
1085 - 47.3 FPE @ 2000 psi
1081
1075
1063
1046
1035
1500 psi remaining

The reservoir is only 7 CI (115 cc) and I was filling it directly.... The efficiency works out to 1.34 FPE/CI (12.2 Barcc/FPE for Voltar1), way better than I have ever achieved before at this power level.... I tried some other pellets right around 2000 psi and recorded the highest velocity for each....

15.9 gr. JSB Exact - 1131 fps (nice sonic crack) - 45.2 FPE
21.0 gr. H&N Baracuda - 1018 fps - 48.3 FPE
25.4 gr. JSB Monster - 946 fps - 50.5 FPE
28.4 gr. EunJin Domed - 892 fps - 50.2 FPE
32.4 gr. EunJin Pointed - 832 fps - 49.8 FPE

The heavier pellets were peaking at 1700-1800 psi so there is room for improvement with a heavier hammer spring.... All the power adjustments are now working the way they should.... The hammer travel adjustment (an adjustable length of the front face) will vary the power down to about 700 fps.... The transfer port restrictor can drop the power as low as about 600 fps.... I didn't see how low I can get with the hammer spring preload, but it works normally.... Neither did I try combining the effects of these three adjustments, I just made sure that they worked properly when moved independantly with the others still at maximum....

This rifle will be fitted with a 22CI tank regulated (initially) to 2000 psi.... That will mean that I will have 69 Bar times 22 CI = 1518 CI of air available to the regulator setpoint.... At 1.34 FPE/CI that works out to 2034 FPE.... or about 40 shots at 50 FPE.... I'm thinking this is going to be one heck of a great gun when it's done.... Mr. Green

Thanks again to Al for cracking this one.... I owe you big time, buddy.... YouAreAGod

Bob

AirGunEric · Site Admin

Funny- I would have thought there would be enough space around the hammer to allow some blow-by, obviously not enough.

Well, there is a lesson here: if you don't want pressure where pressure shouldn't be- make sure there is lots of venting!

69Hotrod69 · Veteran Member

Nice call Al! Clap Clap

Seems the Crosman engineers surprise us again. I allways wondered what that hole was for.

That rifle is going to be amazing! Thumb Up! v2

Your just at the first stage of tuneing and allready getting those results! Nice Work!

69Hotrod69 · Veteran Member

Hey Bob,
When you have a chance hows about a picture in shooting form.

yourdaddyjoe · Supporting Member

Damn! Now I have some guns to do that mod to...

THANK YOU AL! YouAreAGod