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

rsterne · Moderator

I took SeanMP's advice and polished the bore with Bore Brite (red) today, and true to what he said, I picked up a few fps and the groups tightened up.... I tried the RVA at 2.5 turns out as well, with a 3000 psi fill, and got just about what I expected.... Although the first shot wasn't the fastest, the peak of the bell-curve was only at shot 5, and the efficiency was just under 1.0 FPE/CI.... so that's a little too hot.... I retested at 3 and 3.5 turns out, and the results of these three tunes are below.... All started at 3000 psi except the 3.5 turns out, which required only a 2800 psi fill....

The best tune is 3 turns out, which allows me to use a full 3000 psi fill and get 20 shots within a 4% ES and 13 within 2%, using an average of 44 psi per shot.... There are 16 shots within 25 fps between 1004 and 1029 fps, so that makes a pretty decent sweet spot using a 2900 psi fill and a 2200 psi refill, which works out to 1.13 FPE/CI at an average of 95 FPE.... If I was running the gun on a tether, I would fill to about 2700 psi, shoot a 5 shot group, and refill at 2500.... or use a regulator set for 2600.... That would give me 5 shots within about a 5 fps ES (0.5%) by running right at the top of the bell-curve....

When I shot the last string after I reset the RVA to 3 turns out after the days testing, I shot four 5-shot groups.... They were all just ragged holes, but one was exceptional.... It is the first time I have ever had a gun pass the "Feinwerkbau Test"....

I realize this was only at 20', but it's still the only time I could put a bullet in the hole made by a 5 shot group and have it remain in the single sheet of target paper.... The testing and tuning on this gun is now complete until I can get it outside to stretch its legs this summer.... The .257 cal barrel and my new bullet molds should be here this week, so the plan is to work on that next....

Bob

rsterne · Moderator

I got my .257 cal barrel about 10 days ago, did the basic machining on it, and then waited for my bullet molds to get here so that I could cast some bullets, measure them, make a chambering reamer, and finish the barrel off.... That all happened this week, and I got to test the gun for the first time today.... My SCUBA tank was at about 2800 psi, but I did manage to run a few short strings through just to make sure I had enough hammer preload adjustment, which I'm pleased to say I do.... I may not have much extra available once I try a 3000 psi fill, but it looks like it will be enough.... Here are the initial results, using the 73.4 gr. solids I cast from my new Lyman #257420 (65 gr.) mold....

With the preload at my maximum reference point (still shy of coil bind), the maximum velocity I got at 2800 psi was 947 fps (146 FPE), easily over my goal of 130 FPE.... I also tried a few of the 87.6 gr. solids from my RCBS 85 gr. "Cowboy" mold, and they shot 878 fps (150 FPE) at just under 2800 psi.... Even higher peak FPE should be available at 3000 psi, hopefully I'll find out tomorrow after my ShoeBox compressor tops up my SCUBA tank.... The curve at 2 turns out on the hammer spring preload is decent, 7 shots starting from ~2600 psi within 4% ES averaging 890 fps (129 FPE) at an efficiency of over 1.0 FPE/CI.... I shot a few of the 66 gr. hollowpoints made from the Lyman mold, and at less than 2700 psi they hit 965 fps (137 FPE).... I expect I'll need to set the preload somewhere around 1 turn out to handle the 3000 psi fill....

So far, I'm delighted with the results.... This gun should be a long range hammer once tuned up....

Bob

rsterne · Moderator

Now that my SCUBA tank was topped up, I could complete the testing on the .257 cal version of my Hayabusa.... The first step was to tether the gun to the tank and fill it to 3000 psi.... Using each bullet, and starting with the hammer spring at just shy of coil bind, I shot two shots (returning the gun to 3000 psi for each bullet), and in each case, the second shot was slower.... I reduced the preload in one turn increments, always starting at 3000 psi, until the second shot was faster, and then shot a string until the velocity had fallen 4% below the peak.... That occurred 3 turns out from coil bind, indicating that was the maximum usuable preload with a 3000 psi fill.... I also shot a full string with each bullet at 4 turns out, recording every shot that was within 4% of the peak, and then graphed the results.... Here is how the power settings affect the velocity....

Also included on the above graph is an average of the efficiency values at each hammer spring setting.... As is typical, adding preload past a given point (2 turns out) at a set pressure (in this case 3000 psi) only wastes air without any significant increase in velocity.... At 3 turns out, the efficiency averaged just under 1.00 FPE/CI, and at 4 turns out, the average was just over 1.20 FPE/CI, which considering the gun is still putting out about 130 FPE is pretty good, IMO.... The maximum power worked out to just over 160 FPE, with the 87.6 gr. bullets at 908 fps.... I'm extremely pleased with that result.... Here is a graph of the shot strings at 3 and 4 turns out....

With the lighter bullets, at 3 turns out, the first shot was the fastest, indicating too much preload, however with the 87.6 gr. bullet, a bell-curve was starting to appear.... At that power setting, the gun was averaging about 140-145 FPE, and the efficiency was running just over 1.00 FPE/CI.... With the hammer spring preload backed out one more turn, all the bullets produced a bell-curve, but the lighter ones were still missing the first few shots, producing 11-12 shots between 3000 psi and about 2300, with the peak occurring at about 2600 psi.... With the heaviest bullet, the 4% ES string started at about 2800 psi, and produced 14 shots ending at 2000 psi.... All the bullets averaged about 130 FPE, with the 66.0 gr. bullet having an efficiency of 1.08 FPE/CI, the 73.4 gr. working out to 1.12 FPE/CI, and the 87.6 gr. producing 1.24 FPE/CI....

If I wanted to have the string include all shots within a 4% ES, I would have to reduce the hammer spring preload slightly more with the lighter bullets, and that would lower the velocity a few fps and extend the string to about 13 shots.... Alternately, I can leave the gun the way it is, and have 10 shots within 20 fps.... which considering the long range use the gun is likely to see, is probably the better choice.... Those 10 shots average 907 fps with the 73.4 gr. solid (134 FPE) and 940 fps with the 66.0 gr. hollowpoint (129 FPE), and I would stop shooting at 2400 psi, achieving an efficiency of 1.16 and 1.12 FPE/CI repectively.... I still have to test the 77 gr. hollowpoint from the RCBS mold.... and all bullets have to be tested for accuracy at longer ranges before a decision can be made about final tuning.... Here is a photo of the completed .257 Hayabusa, with the barrel and main tube still "in the white".... I won't be doing any bluing until the .308 and .357 (9mm) versions are assembled and tested....

Bob

rsterne · Moderator

I topped up my SCUBA tank and tested the 77.2 gr. Hollowpoints cast from the 85 gr. RCBS 'Cowboy" mold today and added the data to the graph.... Here are the shot strings starting at 3000 psi for all four bullets.... The hammer spring preload was 4 turns out from coil bind for all of these strings....

You can see what is typical of what happens as you increase the bullet weight.... the peak of the curve moves to a lower pressure.... I included all shots above 96% of the peak velocity, which resulted in 14 shots for the heaviest two bullets, 12 for the 73 gr. and only 11 for the 66 gr.... but you can see that the reason for the shorter strings is partly because of the 3000 psi fill pressure cutting off the top of the curves.... That may not matter, as I will likely reduce the ES range to around 2% which will drop the strings to about 10 shots anyway....

All these bullets produce an average of about 130 FPE over the shot string, peaking at about 135 FPE.... which is a ton of energy for a quarterbore.... Really all that remains is to do some accuracy testing to determine which is the most accurate at long range.... I plan to strip the gun and reassemble it with the larger breech, valve, and hammer in preparation for the initial testing of the .308 and .357 cal barrels shortly....

Bob

rsterne · Moderator

I've been working on assembling the .308 version of the Hayabusa over the past few days, and I ran into a problem.... I can't get enough hammer strike to make the velocity peak at over about 2300 psi.... This is despite having a heavier hammer with more travel, and a heavier spring than the .257 version.... The new valve has a larger throat, at 0.312" instead of 0.281", and I used a Disco poppet instead of the MRod poppet on the smaller valve.... After fitting an even heavier hammer spring, again with no success (and the gun was so hard to cock it literally took two hands).... I decided I better pull the valve to have a look, and here is what I found....

The sealing face of the poppet started out dead flat.... Note that I was using the latest Disco poppet, with a hole in the top....

The face of the poppet was extruded into the throat about 0.040".... The stem had slid back, and I thought that might have been partially due to the hole in the top allowing air pressure to act on the end of the stem.... The face of the poppet had completely taken on the shape of the raised seat, and was sealing on a diameter larger than the outside of that seat, which was 0.375".... The head of the poppet was actually belled out to a diameter of about 0.44", and was sealing on nearly the outer edge.... No wonder I couldn't drive it off the seat.... Under load, it was probalby wedging into the throat as well.... I talked to SeanP on the phone, and he informed me that the molding force required for Delrin was 270 lbs, and my calculated seat force was nearly 300 lbs. at 3000 psi, so that is what we think is happening.... the force is causing the Delrin to flow....

I had one of the older Disco poppets, without the hole, and wanted to try that, so Sean suggested that I try fitting a metal ring around it to keep it from expanding, which I did.... I also chamfered the edge below the ring slightly, hoping to prevent the seal diameter from getting bigger than the OD of the seat on the valve....

I put the gun back together, and there was no difference.... Upon disassmbly, I found that the face of the second poppet looked basically just like the first, it had a big groove pounded into it, and was extruding into the throat of the valve.... Interesting, the groove on both poppets is deeper and narrower than the shape of the slightly raised seat on the face of the valve.... There is some serious flowing of the Delrin going on.... I will be pulling the gun apart and reinstalling the valve from the .257 cal version.... The throat is a bit smaller, but at least the hammer will open it....

Bob

rsterne · Moderator

Well, installing the .257 valve at least got the gun working in .308 cal.... At coil bind I got over 200 FPE on the first shot, which makes this rifle more powerful than my DAQ .308 Exile with the same 119 gr. Lee RN bullets.... My SCUBA tank wasn't quite at 3000 psi, and dropped with each fill, so all I could do was some preliminary testing.... but it was quite satisfying....

The gun is quite sensitive to hammer spring preload after 2 turns out from coil bound as that is where you start to get "play" in the spring.... so there was a big drop from 2 turns out to 3, and that happens to be right where I need to be.... I have a 131 gr. hammer with 1.45" of travel driven by a 3.0" long spring made of 0.051" wire.... so the gun is quite hard to cock.... I'll do a bit of playing around tomorrow and see what I can get for a shot string....

I know there is more lurking in this gun once I figure out how to get the bigger valve working.... However, I already accomplished my goal of breaking 200 FPE at 3000 psi....

Bob

rsterne · Moderator

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 · Moderator

I've been pondering the requirements for hammer strike, and this gun has taught me a lot.... A while back I developed a Hammer Strike Database and then graphed the Hammer Energy and Momentum vs. the Force required to knock the poppet off the seat.... That is the seat area times the pressure, plus the valve spring force.... The trends were pretty linear over a large variety of guns, but there is a problem with it.... It doesn't account for the extra hammer strike required to allow for an increase in bore size, and hence the potential FPE, which is ultimately related to the amount of air released by the valve.... As an example, it would predict the same hammer strike required for my Hayabusa in .224, ,257, and .308 cal (and the yet to come .357)....

I had addressed the idea previously, in another thread, that hammer strike must increase with caliber when you change the barrel on a gun.... In an attempt to correlate this, I added a column in my database for the FPE output of the gun, and graphed the Hammer Energy and Momentum vs. FPE.... Once again, the trends are relatively linear over a wide variety of guns.... Using this version of my Hayabusa as an example, although the opening force is still the same (eg. in .224, .257, and .308 cal) the Hammer Energy and Momentum required 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 volume and hence the FPE produced.... not linear, but certainly there is a correlation.... I'm thinking that the two components (opening force and FPE produced) are BOTH part of the criteria needed to determine the amount of hammer strike required.... As yet, I don't know how to "adjust" their relative importance to improve the ability to predict how much hammer strike is required for a given gun.... but I'm working on it....

Bob

rsterne · Moderator

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 · Moderator

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

rsterne · Moderator

I had a small problem with the hammer sticking, so I fixed that, and then adjusted the RVA for the best shot string starting from 3000 psi with the heaviest bullets and then shot strings to 96% of peak velocity with all the different .357 cal bullets I have.... The results are below....

The 67 gr. is a roundball, the 78 gr. is a the JSB pellet, the 90, 117, and 126 gr. are Air Venturi bullets, and the 132 gr. are Lee bullets which I cast and sized to 0.357".... The three heavier bullets all returned a 10 shot string averaging over 200 FPE, with the 132 gr. peaking at 209 FPE, and returning an efficiency of 1.11 FPE/CI, with all three dropping to 2050 psi at the end of the 10 shot string.... The 90 gr. averaged 186 FPE over 9 shots, the 78 gr. JSB pellets averaged 177 FPE over 8 shots, and the 67 gr. roundball averaged 166 FPE over 8 shots, with the first shot being the fastest at 1055 fps.... The efficiency dropped with the weight, and the roundball only managed 0.91 FPE/CI....

Until such time as I figure out how to get the larger valve working, this completes the initial testing of the unregulated version of my Hayabusa with all four barrels.... Here is a summary of the results, all strings to 96% of peak velocity, starting at 3000 psi:

.224 cal - 41.5 gr. - 20 shots at 1012 fps - 94 FPE
.257 cal - 77.2 gr. - 14 shots at 873 fps - 130 FPE
.308 cal - 118 gr. - 10 shots at 833 fps - 182 FPE
.357 cal - 132 gr. - 10 shots at 835 fps - 204 FPE

The .224 and .257 cal share a hammer and breech, and the .308 and .357 cal share another hammer and breech.... At the moment, all are using the same valve, so it only takes a few minutes to change calibers, I don't even have to degas the gun.... This has turned out to be a very successful winter project.... I'm looking forward to getting out into the bush for some long range testing when the rest of the snow is gone....

Bob

rsterne · Moderator

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 · Moderator

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 · Moderator

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 · Moderator

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