My Hayabusa PCP - The Experiment Continues

[SeanMP]

Mine will eventually be completely captured. I just haven't faced it off yet. Mine uses an Oring in a groove (conventional) But yes the delrin disc is completely captured.

This one is .305....I'll let you know but after seeing yours I think it's going to get squashed

Edit....maybe not though. I just did the force calc and it's 256lbs at 3000psi

[rsterne]

Now that my SCUBA tank was topped up, I was able to adjust the RVA to get the best shot string starting from 3000 psi.... I used bullets that were sized to .308" today (yesterday I tested with unsized 119 gr. Lee RN).... Today I used the 118 gr. Lee FN, plus some 100 gr. and 104 gr. Lee .32 cal bullets (cast at 0.313", sized to 0.308") and also some of the new 46 gr. FX .30 cal pellets (made by JSB with a 0.300" head)) that I upsized to .308".... Here are the results at 2.6 turns out from coil bind....



Considering I'm working with the valve from the .257, I'm quite pleased with the results.... The 118 gr. bullets averaged 182 FPE over 10 shots within a 4% ES at 1.15 FPE/CI.... That compares to my .308 DAQ Exile which delivered only 6 shots at 177 FPE (starting from 3200 psi) over a 5% ES, and with an efficiency of only 0.88 FPE/CI.... and that was after I "set" the hammer spring.... Initially, the DAQ only shot 3 shots averaging 163 FPE over a 12% ES (the first shot was 836 and dropped like a stone after that) and with an efficiency of only 0.38 FPE/CI....

The 100 & 104 gr. bullets shot about 169 FPE at an efficiency of 1.08 FPE/CI.... The JSB pellets went supersonic, but the first shot was the fastest at 1170 and it dropped subsonic at shot #6.... The energy was only 135 FPE, and the efficiency was only 0.70 FPE/CI.... If I detuned the gun for those pellets, bringing them down to ~950 fps, I would think it should be possible to get the efficiency back over 1.0 FPE/CI.... but I'm not going to bother, as that will be the goal of my new .30 cal Disco Double with the .300" bore barrel....

Anyway, I'm quite pleased.... I plan on installing my .357 barrel and doing some testing with that, still with the .257 valve installed.... It will be interesting to see what FPE can be achieved with the even larger caliber....

Bob

[rsterne]

Is your 0.305" the throat size, or the OD of the metal poppet?.... My .257 valve has a 0.281" throat and the MRod poppet is a 0.33" OD....

Bob

[Gippeto]

Would like to know where that valve pic came from if you don't mind. :)

Aside...valve in the .32 pcp (and the current .30 qb build) resembles that used in the AT44, but on a larger scale. I like how "tweakable" it is as far as annular area is concerned. Effective valve diameter can be easily altered as well...reducing or increasing requirement for hammer strike as the need takes.

All "that" without having to completely re make the valve. :)

Regards,

Al

[SeanMP]

The valve pic came from the disorganized chaos I call a shop :~)

[Gippeto]

Well then...nicely done Sean.

Al

[SeanMP]

Is your 0.305" the throat size, or the OD of the metal poppet?.... My .257 valve has a 0.281" throat and the MRod poppet is a 0.33" OD....

Bob

Sorry Bob I missed this and there is a correction to be made. The throat is .302. An "O" drill So with runout .303-.304

The poppet head measures .335

[rsterne]

So in between my two valve sizes, but the OD of the poppet (ie the sealing diameter) is the same as the smaller valve with the MRod poppet.... In that case, you will be very interested in the last set of shot strings posted below with the small valve....

I've added a column for the FPE of the gun in my Hammer Strike Database, where I was graphing Hammer Energy and Momentum vs. Opening Force.... and added a second graph for those vs. FPE.... Again, the trends are pretty linear.... There was a problem with just graphing against opening force, because as you put a bigger and bigger barrel on (and hence want more power), you have to knock the valve open further to fill that barrel (about half way before the valve closes is typical).... That means that although the opening force is still the same (eg. my Hayabusa in .224, .257, and .308) the Hammer Energy and Momentum increases.... Here are the numbers for those three, all at 2600 psi (where the shot string peaks)....

Opening Force (0.33" Poppet OD @ 2600 psi) = 232 lbs. (same for all calibers)
.224 cal @ 95 FPE, bore volume 18.1 cc: Hammer Energy 0.737 FPE, Hammer Momentum 0.108 ft.lb/sec....
.257 cal @ 135 FPE, 22.5 cc: 0.886 FPE, 0.118 ft.lb/sec
.308 cal @ 185 FPE, 34.2 cc: 1.272 FPE, 0.151 ft.lb/sec

As you can see, the required hammer strike is NOT just dependant on the seat area and pressure, although they are the only factor in "cracking" the valve open.... Once it's open, the hammer strike to produce enough dwell to keep the valve open to produce the necessary FPE is related to the bore.... not linear, but certainly there is a correlation....

Bob

[rsterne]

Here is a graph showing the Hammer momentum vs. the Sum of (Opening Force plus 2X FPE) for the .224, .257, and .308 versions of my Hayabusa....



The trend is very close to linear as you can see.... However, before this can be used for predictions, there is one big caveat.... All three calibers are tuned in a similar manner.... They all have the valve closing at nearly the same point in the pellet's travel down the barrel (43-46%), and they all have nearly identical efficiencies (1.11-1.15 FPE/CI).... Therefore, the only real variable left is the caliber, hence the bore volume, and the associated FPE.... If any (or all) of these examples were tuned for a different power level, the hammer strike would change.... Whether or not it would stay on the trendline I can't say....

Bob

[rsterne]

I pulled off the .308 barrel today and installed the .357.... In addition, I added a knob to the cocking handle to make the hammer easier to pull back.... That made a HUGE difference to how easy it is so cock (it no longer digs into your hand).... and it also added another 14 gr. to the hammer, bringing the weight to 145 gr.... Here is a photo of the Hayabusa with the hammer cocking handle installed....



It turns out that with the extra hammer weight, the preload adjustment for the .308 cal is almost perfect for the .357 cal with 132 gr. bullets.... I had 2900 psi in my SCUBA tank, and tethered the gun to find out the maximum velocity with the preload at coil bind, with the following results:

90 gr. - 989 fps - 196 FPE
117 gr. - 910 fps - 215 FPE
126 gr. - 888 fps - 221 FPE
132 gr. - 875 fps - 225 FPE

The first shot was the fastest, but the pressure was a bit below 3000, and I had a feeling that if more hammer strike was available that higher FPE numbers could be recorded.... However, the preload has to be dialed back to about 2.5 turns to produce a proper bell-curve.... By the time I determined that, my tank was under 2800 psi, so a graph of the shot string will have to wait until tomorrow after I top up my SCUBA tank with my ShoeBox compressor.... It looks like I should get about 10 shots at 200 FPE with the 132 gr. Lee cast bullets sized to 0.357".... The preliminary efficiency works out to about 1.18 FPE/CI, which I think is pretty darn good at that power level....

I tried a couple of shots with the 78 gr. JSB pellets, still at 2.5 turns out, and it looks like they shoot at about 1000 fps.... I'll do full strings of all the bullets I have once I can fill to 3000 psi.... I also have a mold for a 150 gr. Lee bullet, which I expect will cast at more like 160 gr. in pure lead.... but since I'm still working with the .257 valve they would likely be under 800 fps, so for now the 132 gr. looks like the best choice....

Bob