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PostPosted: Thu Jun 13, 2013 7:30 am 
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Looks just like the "hammer slap" mod made for Condors years back, although serves a different purpose...

Very interesting numbers, maybe I will have to buy myself a Disco, have always wanted one just to get more bang for my buck on scuba tank fills...Could get a lot of shots with a disco from 2750PSI down to 2000PSI, especially with those kinds of numbers/setup 8)

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PostPosted: Thu Jun 13, 2013 11:39 am 
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Could get a lot of shots with a disco from 2750PSI down to 2000PSI,

Just remember to beef up the valve mounting screws.... The stock ones only have a 2:1 safety margin above 2400 psi from the best info we currently have.... I wouldn't fill a Disco above the yellow zone on the gauge (2400) without installing stronger screws....

Bob

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PostPosted: Thu Jun 13, 2013 2:22 pm 
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Well, I learned a valuable lesson about the O-ring buffers, today.... If the hammer isn't hitting them, they can shift out of place and cause weird results.... I began to suspect that last night, and bstaley suggested it this morning, but I had already confirmed it.... I think the slight air blast coming out around the stem of the valve pushes them back a bit, or maybe just makes a space between them if the hammer isn't already contacting them as it would be before that blast of air occurs if the buffer was even partially engaged.... In addition, I made a new Lift Indicator Rod, even lighter and with a thinner head than the original.... This one is made from 5/32" OD aluminum hobby tubing, and only weighs 1.4 grams and only requires 1/2 turn adjustment on the preload.... The larger diameter means it doesn't wiggle around in the hole in the RVA adjusting screw, and the larger O-ring tends to stay nice and straight, allowing much more accurate and consistent measurements.... I then redid my previous lift measurements, and took a bunch of new ones, with the following results....

Image

I have confirmed that at 4 turns in, with either O-ring stack, the hammer does NOT contact the buffer (or so lightly as to have no effect), providing the O-rings haven't shifted.... Therefore, those curves on the previous graphs should be ignored.... Anything happening there is a result of the buffer not remaining properly in place.... In addition, the previous chart I posted about the lift numbers with the 90D buffer are incorrect, the numbers above are the accurate ones....

Note that the lift at 1000 psi with no buffer in place changes 0.022" between max. stroke (full CCW) and 4 turns in, or about 0.005" per turn, and that should be linear.... That means that at 3 turns in, with no buffer, the lift at 1000 psi should be about 0.086".... I made another test, with the 90D buffer at 3 turns in, and the lift was 0.084", so the buffer is either not in contact, or it is just barely touching it at 1000 psi.... It would NOT be producing any changes to the shot string, so again any difference between that string and the unbuffered one would be due to the stack moving around.... I also tested the 70D buffer with the backer ring at 3 turns in, and the lift was 0.075" at 1000 psi.... This indicates that the hammer is just making contact at that pressure, but it would not be making contact with the buffer at over 1200 psi.... so the data for that string (unfortunately, the best string I had initially) may be somewhat suspect.... Perhaps that is why I couldn't duplicate it last night.... On the other hand, if the hammer is contacting the buffer at 1000 psi and below (only), that may be the reason that first string extended down to 850 psi....

Now that I have a better indication of what range of adjustments will and will not work, I am going to go back and retest both the 90D and 70D (with backer) stacks at the appropriate settings, but this time with 1/2 turn increments.... I'm hoping for a lot more consistent results....

Bob

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PostPosted: Thu Jun 13, 2013 6:59 pm 
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I completed the second set of tests, changing the striker setting by only a half turn at a time instead of a full turn.... I also eliminated the settings where I was sure the buffer was not playing a role.... All strings were started at 2000 psi, and the Disco hammer spring was set just shy of coil bind as before.... and only shots within a 4% ES are graphed.... The four 70 Durometer O-rings had a 90D Backer ring under the stack.... and here are the results....

Image

Basically, once the striker is screwed in 2 turns CW or more from the fully CCW position, it is ineffective in altering the shot string to any significant degree.... These results are different for the 3 turns out curve (blue line) which I found in the first test.... My only explanation is that the buffer in that test was moving out of place slightly, and interfering with the hammer in just the right way to skew the results.... That curve was a lower velocity, longer, and flatter, but since I haven't been able to duplicate it in several tries, all I can say is that it was a tease, unfortunately.... The 2 and 3 turn in shot strings are virtually identical to the unbuffered results....

When we explore the striker adjustment range from maximum CCW (minimum lift) to 2 turns in, however, we have some very interesting things happening.... As the velocity drops, the efficiency increases, and the strings get longer.... At 1.5 turn in, the average velocity is 775 fps (at 1.18 FPE/CI), and a 1 turn in, it drops to 718 fps (at 1.36 FPE/CI).... In both cases, a large portion of the first part of the shot string appears to be missing, an indication that the hammer strike is too great for the 2000 psi fill pressure.... For both of those strings, further experimentation is needed.... At 1/2 turn in, the velocity is only 617 fps, but the gun got 32 shots within 4% ES, and the efficiency was 1.65 FPE/CI, very efficient for a 12 FPE gun.... If you remember from the first tests with the 70D buffer, at maximum CCW, the velocity was about 430 fps and the gun did 65 shots at 2.11 FPE/CI between 1650 psi and 1000.... This soft, tall buffer is excellent for drastically reducing the power of the gun and raising the shot count and efficiency.... If that is what you are after, this is something you should definitely consider....

Now to look at the stiffer buffer, consisting of four 90 Durometer O-rings.... Here are the results....

Image

With this stiffer buffer, and without the extra height of the 0.055" thick backer ring, the buffer was basically ineffective once the adjuster was past 1 turn in.... The top group of curves pretty much mirror those of the unbuffered gun at the same adjustments, although for some reason they seem to peak at a slightly higher velocity, although no higher than the unbuffered gun did at maximum.... The efficiencies are similar as well, so IMO no advantage can be found operating in that adjustment range....

Once again, however, when we explore from maximum CCW (minimum lift) over the first part of the striker adjustment, we see more shots at increased efficiency, but at lower velocity.... The shot string at 1/2 turn in (791 fps average) started out with the first shot the fastest, so it definitely needs to be explored with less hammer spring preload.... With the striker at maximum CCW, the velocity averaged 671 fps, and it looked like it too, could benefit from a bit less hammer energy for the 2000 psi fill.... The efficiency of that 15 shot string was 1.30 FPE/CI, and I have a feeling that both can be increased a bit.... However, when you consider that the 1 turn in string with the 70D buffer was higher velocity AND more efficient, I have my doubts if the 90D buffer will show any advantages over the softer one....

There are a couple of general observations I have to make.... When the striker adjustment first starts to have a serious affect on the velocity, it appears that the shot string shifts to the left, ie it peaks at higher pressure.... In an unbuffered gun, that usually indicates too much hammer strike, and that is likely the same case here.... Only adjusting the preload to a lower value will let us find out if there is more shots and efficiency hiding there.... Once the velocity is reduced further, however, the shot string returns to the original peak pressure, and eventually, as the velocity is lowered enough, then the fill pressure must follow, just as in detuning by hammer energy alone.... While the basic idea of reducing lift directly by decreasing the striker engagement with the valve is simple in concept, and very effective.... it still needs that fine tuning of trying various combinations of hammer spring preload and/or fill (and refill) pressure to find the optimum setting....

When time permits, I plan to concentrate on those parts of the envelope where less hammer strike is needed to optimize the results.... In the meantime, there is certainly lots here to chew on and discuss....

Bob

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PostPosted: Thu Jun 13, 2013 7:01 pm 
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rsterne wrote:
Quote:
Could get a lot of shots with a disco from 2750PSI down to 2000PSI,

Just remember to beef up the valve mounting screws.... The stock ones only have a 2:1 safety margin above 2400 psi from the best info we currently have.... I wouldn't fill a Disco above the yellow zone on the gauge (2400) without installing stronger screws....

Bob

I mean using my scuba tank to fill the disco to 2000PSI when the tank gets down to 2750PSI as that is the fill pressure I use for most of my PCPs

I would get a lot more use out of the tank

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PostPosted: Thu Jun 13, 2013 8:05 pm 
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Gotcha!!!....

Bob

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PostPosted: Thu Jun 13, 2013 10:47 pm 
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I had a chance this evening to do some testing of preload changes on the 90 Durometer stack for the striker position that was 1/2 turn out.... That tune had a shot string that started high and declined, so I wanted to see what would happen if I reduced the hammer spring preload, if the gun would react in a "normal" fashion even with the buffer.... Well, as I expected, it did.... The colours have changed on this graph for clarity, so don't use them to refer to earlier graphs....

Image

All the solid lines are at maximum hammer spring preload, as before.... The black line is with the striker full CCW (0 turns), the solid red line is 1/2 turn in on the striker, and the blue line is 1 turn in on the striker.... The other two red lines show what happens with the preload reduced two and four turns.... As you can see, the peak velocity drops and shifts to a lower pressure, reacting just like a conventional unregulated PCP, as the preload is reduced.... In addition, the efficiency increases, and the shot count increases, again as per usual.... The interesting thing about the efficiency is that it increases from top to bottom on that graph, starting at 1.06 FPE/CI for the blue line, and progressing to 1.30 FPE/CI for the black line.... I have no reason to believe that any "magic" will happen in between, although in between tunes are certainly possible.... As an example, if you wanted to tune for the flattest curve peaking at 800 fps, you would use a striker setting roughly 3/4 of a turn in CW, and a preload likely in the neighbourhood of 2 turns out from coil bind.... and you could expect about 12 shots at an efficiency of about 1.20 FPE/CI.... Using a full size Disco tube, that would be about 24-25 shots within a 4% ES.... The problem is, that is basically no better than you can get with a stock Disco.... From what I have seen so far (and I'm running out of ideas), the 90 Durometer buffer doesn't seem to offer a significant improvement over stock.... I detuned a Disco with just an RVA (preload adjuster) and achieved 33 shots at 18.6 FPE within 4% ES from 1800 psi down to 1000.... That is 614 FPE from 452 CI of air, which works out to 1.36 FPE/CI.... That is more power AND more efficiency than anything I've seen so far with the 90 Durometer buffer.... It is possible, of course, that shortening the valve stem and increasing the hammer stroke might provide better results.... I'm still hoping that the 70 Durometer buffer will provide greater efficiencies as well....

Bob

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PostPosted: Fri Jun 14, 2013 5:18 pm 
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I decided that for the Preload testing on the 70 Durometer buffer I would try removing the 0.055" thick Backer Ring.... Here is the test at Maximum CCW on the striker, and maximum preload (just shy of coil bind).... shown on the graph as the black line with square markers....

Image

You can see that my intuition was pretty good about using the Backer Ring to check out the lower end of the velocity range possible using a bstaley buffer.... Without it, and with the striker set fully CCW (minimum lift) the average velocity of the string was 750 fps, about halfway between the 1 turn in and the 1.5 turn in strings.... However, this is perfect to explore reducing the preload, as most of the first part of the shot string is misssing.... The plan is to try a few reduced preload settings with this striker adjustment, and then wind it in 1/2 turn and test again.... Incidently, once again on this graph, the efficiency increases from top to bottom, from 1.07 FPE/CI at 2 turns in to 1.65 FPE/CI at 1/2 turn in, with the "Max. No Backer" string coming in at 1.20 FPE/CI....

Bob

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PostPosted: Fri Jun 14, 2013 9:52 pm 
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I completed the preload adjustment trials this afternoon, working on the strings that were "left shifted" ie the first shots were the fastest when the hammer spring preload was at maximum.... Here are the results for the stack of four 90 Durometer O-rings....

Image

The string at 1/2 turn in on the striker (solid red line) was shifted left.... I shot additional strings at 2 turns and 4 turns out on the preload, shown in the dotted and dashed red lines.... The string at 4 turns out was the longest and the most efficient, returning 14 shots averaging 738 fps with an efficiency of 1.25 FPE/CI.... The highest efficiency overall was still the minimum lift string (black line - striker fully CCW), which was 15 shots at 670 fps. and 1.30 FPE/CI.... That is decent efficiency, but not as good as I shot with a stock Disco with the power just dialed down to the same level with an RVA.... On to the stack of four 70 Durometer O-rings (without the backer ring)....

Image

The first thing to note is that at 1 turn in on the striker (the blue line), the shot string is almost identical to the same curve using 90 D Orings (top), and indeed virtually identical to the unbuffered gun at the same setting.... In other words, by that time the buffer is pretty much ineffective.... The set of red lines (1/2 turn in on the striker) are the same as on the first graph, solid is maximum preload, dotted is 2 turns out, and dashed is 4 turns out.... The most efficient of those was the latter, 16 shots at 758 fps with an efficiency of 1.24 FPE/CI.... The black lines are at fully CCW on the striker, using the same line types as above.... Once again, the curve at 4 turns out on the preload was the most efficient, giving 19 shots at 713 fps (16 FPE) and 1.31 FPE/CI.... Once again the efficiencies were beaten by a stock Disco detuned with a simple RVA, but in this case there were more shots in the string within a 4% ES than I have been able to achieve before at these power levels.... The bottom string on that graph would be 38-40 shots using a full size Disco tube....

I can now offer the following conclusions for my testing of the four #113 O-ring bstaley buffers in a stock Disco fitted with a Challenger hammer and RVA....

1. The 90 Durometer O-rings provided a wider range of velocities for the same range of striker adjustment.... eg. 1 turn was ~175 fps compared to ~125 fps....

2. The 70 Durometer O-rings required an additional spacer to get under 700 fps, but when used with a 0.055" thick backer ring could be adjusted down to about 440 fps (6 FPE).... I preferred the 70D....

3. With both buffers, as the buffer first becomes engaged, the peak of the velocity curve shifts to higher pressures, and must be compensated for with reduced hammer spring preload.... This is over a range of about 1 turn for the 90D buffer and about 1.5 turns for the 70D buffer....

4. I was unable to achieve increased efficiency during this first stage of buffer engagement, compared to what could be achieved at similar velocities with a simple RVA.... At the lower power levels, however, longer than usual shot counts were obtained with the 70D buffer....

5. As the buffer becomes fully engaged, the velocity drops rapidly, and the peak of the curve shifts back to the original pressure range.... Eventually, as the velocity is decreased further, the peak shifts to lower pressures, and the fill pressure must be reduced accordingly....

6. During this second portion of the buffer use, with the 70D buffer with backer ring, the efficiency climbed to higher levels than I have acheived in a Disco with a simple RVA, peaking at 2.21 FPE/CI, an extremely high value, at 6 FPE.... These high efficiencies were obtained with very large shot counts as well....

The bstaley buffer, when used in a stock Disco, provides the ability to change the velocity over a wide range, in a very quick and simple manner, without having to adjust the fill pressure.... I didn't find any gains in efficiency unless the power was reduced below 15 FPE using the 70D buffer.... although some lengthening of the shot strings occurred when settings were optimized for any given velocity.... I personally preferred the 70D buffer over the harder 90D O-rings.... although I didn't test the 90D below 670 fps.... When the Disco is detuned to below 600 fps using the 70D buffer, the efficiency skyrockets, and the shot strings soar....

All in all, an interesting experiment.... I learned a lot....

Bob

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PostPosted: Mon Jun 17, 2013 11:11 pm 
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Today I got a chance to try a buffer made from three 70 Durometer O-rings instead of four.... That required replacing the flanged striked in the Challenger hammer with one made from a 1/4-28 SHSS with the point ground flat.... The hammer ended up slighty lighter, but with the striker set flush with the end of the hammer, the stroke increased from 0.50" (with the flanged one fully retracted CCW) back to the stock travel of 0.58".... This increased the velocity of the shot strings, making the first shot pretty much the fastest, and moving the energy of the gun up to 24 FPE with the striker extended a turn, which made the buffer ineffective.... I left the hammer spring preload just shy of coil bind and shot a string with the striker flush, extended CW 1/2 turn, CW 1 turn, and also with the striker below flush (CCW) by 1/2 turn.... Those results are show in the graph below as solid lines.... The efficiencies are all below 1.0 FPE/CI, as we would expect with the excessive hammer strike eliminating most of the first half of the shot strings....

Image

The buffer is ineffective with the striker 1 turn CW, and having little effect at 1/2 turn CW, but becomes effective when flush, and the velocity continues to drop as the striker is recessed in the face of the hammer.... I didn't try it further CCW than 1/2 turn, however, as I was interested in velocities not too far below stock.... I then optimized the hammer spring preload for three striker settings, with the buffer just disengaged, starting to engage, and well engaged, and those are the dotted lines.... The colours are the same as the strings taken at maximum preload.... The dotted red line is fairly close to stock Disco power and shot count, although down a bit on efficiency at 1.07 FPE/CI.... The dotted green line is with the striker flush with the end of the Challenger hammer, with the preload set 5 turns out from coil bind.... That turned out to be the optimum setting for a 2000 psi fill, and the string is 17 shots at 18 FPE for an efficiency of 1.29 FPE/CI.... The dotted black line was with the striker 1/2 turn recessed in the hammer face and the preload out 6 turns, and returned 20 shots at 16 FPE with an efficiency of 1.34 FPE/CI.... Once again, these efficiencies, while pretty decent, are no better than what I can get with a simple RVA in a stock Disco.... However, you can still use a 2000 psi fill, and because of that, the strings are longer....

In reality, there is no practical difference between today's testing and what I did last week with the stock Challenger striker and one more O-ring in the buffer.... Either setup can be adjusted for about the same velocities and efficiencies.... although today's strings are 1 shot longer than with the taller buffer.... When you consider that with a full size Disco tube, the shot count will double from the above.... 40 shots within a 4% ES at 16 FPE is a pretty decent string starting from 2000 psi and shooting down to 1150....

Bob

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Airsonal;
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PostPosted: Sun Jun 23, 2013 4:31 pm 
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Yesterday I took my test gun apart again and removed another O-ring from the buffer, so it is now just two #113s of 70 Durometer.... In order to allow the hammer to engage the buffer, I simply wound the setscrew I am using for a striker out 3 turns (0.108") to allow for the missing O-ring.... Note that as you back the striker out CCW below flush, you increase the hammer throw (to where it first contacts the stem) beyond stock but reduce the preload by the same amount.... At 3 turns below flush, the hammer stroke is now 0.69" and the preload is effectively at 3 turns out, even though the spring remains at coil bind when cocked.... After a few shots to determine where the buffer started to engage the hammer face (2 turns below flush) I shot some strings at maxmum preload.... and then at reduced preload on the last string to move the curve back below 2000 psi....

Image

If you look at the top three curves, you get a perfect picture of what happens as the buffer progressively engages the face of the hammer.... The blue line, with the striker recessed 2 turns into the hammer face, shows the buffer not engaged at all.... The red line, at 2.5 turns recessed, show the buffer starting to engage on the 4th shot in the string, and surpressing the velocity in the second half, shortening the string by 2 shots.... The solid green line, at 3 turns below flush, shows the buffer with increasing engagement, and the entire first half of the shot string is missing, it would require filling to over 2000 psi to see it.... or reducing the hammer spring preload to move the curve to the right.... That is what is taking place with the dotted green line, which is still 3 turns below flush on the striker, but has the preload backed out 5 turns to create an entire shot string without filling past 2000 psi....

As it turns out, I now have three shot strings all at around 750 fps with the preload optimized, but with buffers of 2, 3, and 4 O-rings of 70D.... When I look at the data, I find the following:

Four 70D: 16 shots @ 758 fps (18.2 FPE) @ 1.24 FPE/CI (equals 32 shots in full size Disco tube of 135 cc)
Three 70D: 17 shots @ 748 fps (17.8 FPE) @ 1.29 FPE/CI (equals 34 shots)
Two 70D: 15 shots @ 754 fps (18.1 FPE) @ 1.40 FPE/CI (equals 30 shots)

It is dangerous to drawn any firm conclusions from such a statistically small sample, particularly when the average fps and FPE are not identical.... For example, the small decrease in velocity from 758 fps down to 748 fps could account for part of the increase in efficiency from 1.24 to 1.29 FPE/CI, and maybe for the extra shot as well.... However, there seems to be a slight trend towards increased efficiency with the shorter, and therefore stiffer buffer, but maybe at the cost of a lost shot or two.... Statistically speaking, they are pretty much a wash, so you would be hard pressed to make a choice between them.... When you compare the above with what I got by detuning a stock Disco with just an RVA to about the same power, there is again nothing to choose from.... I got 33 shots at 18.6 FPE within 4% ES with an efficiency of 1.36 FPE/CI from 1800 psi down to 1000....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
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PostPosted: Sun Jul 07, 2013 4:10 pm 
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Yesterday I got the chance to rip apart my test gun and mod the Disco valve.... I drilled the throat to 0.234" (still the stock 0.156" stem), and bored out the exhaust port with a 5/32" mill on a 20* angle.... By the time I was done, both had an equivalent diameter of 0.174".... I drilled the transfer port to 0.162" (about as big as you can go without danger of the wall kinking), but out of curiousity (and because I only have one .22 cal barrel) I left the barrel port stock at 0.134".... I was therefore quite surprised when the gun made 31 FPE with 14.3 gr. pellets.... I didn't record a shot string at maximum preload because the 2nd shot was the fastest at 988 fps, but I shot strings at 2 through 8 turns out on the RVA and here are the results....

Image

The average power is 28.3, 25.7, 23.6 and 21.0 FPE.... and the efficiency is 1.02, 1.17, 1.19, and 1.12 FPE/CI respectively.... The pressure shown in the above graph is only approximate, just to give you an idea of the pressure range for each string.... the starting pressures are very close.... These tests are only to establish a baseline for the testing using a bstaley buffer consisting of three 70 Durometer #113 O-rings.... I am using a Challenger hammer with a 1/4-28 SHSS with the point ground flat as a striker, a Disco hammer spring, and a Challenger RVA.... The above tests were conducted with the set-screw flush with the front of the hammer, so the stroke was 0.58" which is stock for a Disco....Remember, for a full volume Disco reservoir, the above shot counts would double....

We're really busy in the Motel right now, so I have no idea when I will be able to get to doing the bstaley tests, unfortunately....

Bob

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Airsonal;
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Proud Member of the 2000+fps Club!


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PostPosted: Thu Jul 25, 2013 10:48 pm 
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I finally got a chance to get back to testing the bstaley Disco with the Modded Valve.... I installed a buffer consisting of three 70 durometer #113 O-rings, and started with the striker set Flush with the face of the hammer.... I then turned it in 1 turn CW, at which point the buffer is basically not doing anything.... I shot a string at 2 turns out on the RVA to compare to the unbuffered setup in the last graph.... I then turned the striker out CCW in 1/2 turn increments, and readjusted the hammer spring preload so that the best curve was obtained using a 2000 psi fill.... All shots over 96% of the peak velocity are shown on the graph below....

Image

At 1/2 turn in on the striker, the buffer starts to engage the hammer after the first 2 shots.... Both these strings are lower in efficiency than the unbuffered version.... I was particularly interested in the (purple) string with the striker set flush, as the velocity is almost identical to a stock Disco, averaging 850 fps (23 FPE) with the 14.3 gr. JSB Express pellets used throughout these tests.... The string was 10 shots, the same as what I got in the very first tests with a stock gun, but the efficiency was less, at only 0.98 FPE/CI instead of the 1.05 FPE/CI for a stock Disco.... Despite the fact that we were starting with a gun with much better flow and capable of nearly 100 fps more that stock, the bstaley buffered version fell short of the efficiency of even a stock Disco....

When the striker was withdrawn another 1/2 turn, the shot string increased to 13 shots, but the efficiency was still not as good as previously obtained.... At 1 turn out CCW from flush on the striker, the gun returned 20 shots averaging 709 fps (16 FPE) at an efficiency of 1.36 FPE/CI, which is very similar efficiency to other strings obtained using various buffers at the same velocity.... The bstaley buffer system, at least in a Disco utilizing a 2000 psi fill, really seems to come into it's own when the gun is detuned to 700 fps or below.... Unfortunately, at higher power levels, I was unable to get any improvement in efficiency compared to simple detuning using just an RVA.... It does permit filling to higher pressures than just using an RVA, and in some circumstances that can lead to a couple more shots.... but I was unable to wring any improvement in air usage out of any of the versions I tested unless the power was reduced substantially....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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