My Hayabusa PCP - The Experiment Continues

[SeanMP]

Okay Todd I'll take you up on the offer for 3 disco screws. We'll see what pressure they are really good to. I may as well try a standard QB as well.
I have H-K screws here in #8 and #10 but I could try standard high alloy as well. If I'm gonna get wet.... May as well take a bath. :)

[rsterne]

Sean, I know you've been away, but any progress on the hydrotesting?.... particularly interested in the Disco valve screws.... It would be nice to find out they will stand 6000+ psi without failing, which would be a 2:1 safety margin at 3000.... That seems to be everyone's concern with using that pressure in a Disco....

Bob

[SeanMP]

No but it's on the list and I'm keen on getting some of this real world testing stuff done and published. I was overly optimistic about what I could get done on a few stolen sundays off. It would be nice to clean up some of the conjecture and break some Sh!t.

[rsterne]

As shown above, the Disco poppet material wasn't strong enough for the throat diameter and pressure of the .308/.357 valve I made.... Sean got me some PEEK material to make a new poppet, and explained how he made his.... Today I made my first poppet, and I'm VERY pleased with the way ti turned out.... I used a piece of 5/32" Drill Rod for the shaft, and lengthened the spring guide part of the poppet to give more room for the stem.... The PEEK machines nicely, but it's a bit strange to drill, it gets the drill quite hot, so I found it better to use a very low speed.... If the drill was very sharp it may not have had that problem.... In any case, here are the photos of the old and new poppets and the valve....



The head of the new poppet is smaller on the OD and streamilined into the valve spring for a bit better flow as well.... The stem is cut away to 1/8" the same as I did on the Disco poppet.... The valve throat is 5/16", feeding a huge 9/32" exhaust port....



I'm really looking forward to trying this valve in the Hayabusa again, as it never really got a chance to show what it could do with the problems of the previous poppet.... The hammer had great difficulty in unseating the very much deformed valve....

Bob

[rsterne]

When I pulled the .224/.257 valve out of the Hayabusa this morning to install the new .308/.357 valve I found that the MRod poppet was deformed slightly from the load.... Here is a photo after a few hundred shots....



The throat of the valve is 0.281", and you can see that the OD of the poppet is no longer a cylinder, it is belled out slightly on the end from the forces involved.... The original OD was 0.330" and it is now 0.350".... At 3000 psi, the force on the poppet was 256 lbs, assuming a 0.33" sealing diameter, and may well now be greater than that, but the fact remains that was too much for the poppet to withstand without distorting....

I know from past experience that a 1/4" throat on an MRod valve works fine, but pushing the throat ID to 9/32" is evidently overstressing the poppet material.... It may stay like this forever, not getting any worse.... or it might not.... Nice to know, anyway....

Bob

[rsterne]

I finally got around to fitting the big valve in the Hayabusa today with a poppet that actually works!.... The new poppet is made from PEEK, which is a much harder material than Delrin.... I had a problem with the original poppet extruding into the large 5/16" valve throat at 3000 psi, which then required huge additional force to knock it off the seat.... The previous testing in .308 and .357 cal had to be done with the valve from my .224/.257 cal version, so the gun barely broke 200 FPE.... With the new valve in place, it now hits almost 240 FPE, and I still have a stronger hammer spring yet to test.... Today's testing was done with a 3" long, 3/8" OD x 0.051" wire spring just shy of coil bind, filling to 3000 psi.... Here are the results....



The gun now drives a 67 gr. roundball over 1100 fps, and the 78 gr. JSB and EunJin pellets at over 1060 fps.... With all three of those, the first shot is the fastest, so hammer preload is too much to produce a proper shot string.... In fact, you have to get up to a 132 gr. bullet to show a first shot that is slower than the peak velocity.... With that bullet, the velocity hits nearly 900 fps (234 FPE), and with a 154 gr. bullet I am starting to get a normal bell curve, peaking at 835 fpe (238 FPE).... One thing that surprised me was the efficiency of the gun at this power level.... The gun is using about 100 psi per shot (460 cc reservoir), which works out to 1.21 FPE/CI with the heaviest bullet, dropping gradually to 1.13 FPE/CI with the 117 gr.... The 90 gr. bullet got 1.01 FPE/CI, and as expected the pellets and roundball were lower, at 0.90 FPE/CI for the pellets and 0.82 FPE/CI for the roundball.... Reducing the hammer spring preload to produce a bell curve would raise that however, even with the lightest rounds....

This version of the Hayabusa has now been developed to the point where pellets are now too light, and in fact even the 90 gr. Air Venturi HollowPoint is really too light.... The gun really needs bullets over 110 gr. to make use of the power available.... I plan to test the heavier bullets with a stronger hammer spring, just to see how far I can push the FPE, but in fact as a useful gun, this hammer spring is just about perfect, and with bullets in the 117-132 gr. range the preload is a bit too much to produce a proper shot string at the best efficiency....

Bob

[rsterne]

I tried the stronger hammer spring, which is 3" long, 3/8" OD x 0.059" wire, and at coil bind I could barely cock the hammer.... Fortunately, for some reason, the velocity actually increased with a couple of turns less preload.... Here are the best numbers I got at 3000 psi.... This is the first gun I have had that broke 250 FPE....



The best looking hunting bullet of the ones I have is the 132 gr. Lee 358-125-RF (it's supposed to cast at 125 gr.) which has quite a large meplat.... so I hope it proves to be accurate.... After the flat-out testing I changed back to the other spring and reduced the preload a turn and shot a string with them, starting from 3000 psi and ending at 2200....

856
872
875
876
870
866
862
859
856

Maximum Energy: 225 FPE
Average Velocity: 866 fps
Average Energy: 220 FPE
ES: 20 fps (2.3%) over 9 shots
Efficiency: 1.28 FPE/CI

So, I gave up 9 FPE (4%) to get 50% more shots with extremely good efficiency.... I think that is an excellent trade off.... The next step for the Hayabusa is to install the .308 cal barrel and find out what it does in that caliber with the new valve.... By the time I'm ready to test, hopefully the mold for my new Boattail bullets will be here and I can see how they work....

Bob

[rsterne]

I installed the .308 barrel today and tested a few bullets and settings.... Here are the shot strings with the 118 gr. Lee which had previously produced the best accuracy in my DAQ....



The gun is very sensitive to small changes in hammer spring preload, those three curves span only one turn of adjustment.... Just shy of coil bind, the first shot is the fastest at 207 FPE, and efficiency over the 6 shots is 1.03 FPE/CI.... At one turn out, I have 11 shots averaging 184 FPE within a 4% ES and the efficiency has increased to 1.22 FPE/CI.... The first 10 of those shots are within a 2.5% ES, and 7 of them are within just 1%, with 3 in a row being identical at 847 fps.... This gun is slightly more powerful than my DAQ, and a lot more efficient at the same pressures.... As a comparison, my DAQ gets only 5 shots averaging 180 FPE at an efficiency of 0.88 FPE/CI, and that was after I tuned it.... The way I got it, it lost nearly 100 fps over the first 3 shots at an efficiency of 0.38 FPE/CI, but with no more power....

For hunting a good tune is 1/2 turn out.... The first 6 shots are within 7 fps ES (0.8%) and average 193 FPE.... The mid-portion of the shot strings with this bullet are the flattest I have ever seen in a big bore.... Just for the heck of it, I fired a few 46 gr. JSB pellets which I had upsized to 0.308" diameter and they shot between 1190-1198 fps, easily supersonic.... Talk about LOUD !!!

Bob

[AirGunEric]

Seems all the larger-bore airguns are loud- i.e. barely able to tell the difference between them and a regular powderburner- I have a 9mm/.357 that is ridiculous.

Can you use airguns in BC for anything larger than varmints these days?

[rsterne]

To be honest, I don't know.... They don't address airguns at all in the regs directly....

Bob