Not being funny- but as the end result was a "detuning" of the gun to gain shot count- did you do the same tests using the RVA and hammer adjustment screw to achieve the same velocities? I'm not suggesting anything in particular, but if you didn't de-tune the gun to, for example, 430fps with the already existing parts before adding the washers and check the shot count- what we have is a nice graph with no actual comparison to a "before" state.
This specific gun, no, but I have a fair amount of experience with Discos and what they can and cannot do by simply detuning them with an RVA.... As an example, I detuned a dead stock Disco with an RVA to 18.6 FPE and got 33 shots within 4% ES.... The fill pressure was 1800 psi and the gun had to be refilled at 1000 psi.... That works out to 614 FPE total from 452 CI of air, an efficiency of 1.36 FPE/CI.... Compare that to the "blue" (3 turns in) string with the O-ring buffer, doubling the shot count to allow for the 135 cc Disco reservoir instead of the 65 cc available with the 2260 tube.... The efficiency was similar, at 1.39 FPE/CI, but the shot count would be 50 shots, because the string started at 2000 psi and extended all the way down to 850.... a much wider pressure range than I have ever observed in any unregulated PCP.... Simply put, the gun with the bstaley mod gave 50% more shots within the same 4% ES....
Looking at the string of 65 shots averaging 438 fps, I don't have a direct comparison to an unregulated Disco.... simply because it isn't practical to detune one that far with just a hammer strike adustment, in fact I don't think you could do it even with a clipped 2240 spring.... I recently tested this very same gun in stock Disco trim (same 2260 tube), with a 0.070" transfer port, and I got 23 shots at 626 fps within 4% ES, starting at 2000 psi and ending at 1050.... but the efficiency was only 1.10 FPE/CI.... I will eventually be testing it with a Challenger transfer port (0.047") and expect to be close to 500 fps, and will report on that when the testing is complete.... I did build one non-PAL 2260, using a stock Disco valve, and in order to get the velocity under 500 fps I had to use a regulator set to under 500 psi.... The efficiency was only about 1.0 - 1.1 FPE/CI.... The efficiency of the "black" tune with the bstaley buffer was 2.11 FPE/CI, and I have NEVER had any gun break the 2.0 FPE/CI mark before.... THAT really made me sit up and take notice....
I have no horse in this race.... In fact, I had serious doubts about the bstaley mod, and wondered if part of the success was the detuning that was taking place.... The claims were that the shot strings were flatter and longer for the same amount of air used, ie more efficienct.... So far, my results seem to be bearing that out.... However, it would appear that to obtain these results, you have to give up about 20% in FPE compared to what the gun will shoot without the buffer.... For many, that will not be of any use.... I tend to max. out my experiments to see how much power they will deliver, and then detune them a bit for use.... However, the detuning I do is seldom even 10%, let alone 20%.... At this point, I can't tell you if I will find a place in my guns for a bstaley mod or not....
There are two things I REALLY like about this tuning method, however....
1. By using a hammer with an adjustable striker in this manner, you can tune the gun over a wide velocity range without having to drastically change the fill and refill pressures.... If you try and detune just with hammer strike (and I don't care whether you do it with springs, travel, or hammer weight), by the time you cut the power of a PCP in half, you will have to drop the pressure range you use.... The bstaley tune allows the velocity to be adjusted over a wide range without a corresponding drop in pressures....
2. This ability to reduce velocity while maintaining a reasonable fill pressure (or maybe the same fill pressure), can be taken to extremes, something I haven't seen in conventionally tuned PCPs.... Try and retune one to non-PAL velocities (using an RVA) and the fill and refill pressures drop wayyyyyyyyyyyy down.... That causes the shot count to drop, because you aren't getting all of the benefit of the lower power.... I actually got over 110 shots from 65 cc, and the velocity was still 420 fps when I quit.... and 65 of those shots were between 430 and 447 fps.... That's only a 10 psi drop per shot on a tube half the volume of a Disco.... Something is going on here that needs further investigation....
Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count!
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....
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
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count!
Let me ask once other question- interference- ? Do the o-rings have the ability to twist/shift in the tube and thereby block the hammer from contacting the valve stem completely, or are they being fastened together in some way to prevent this, or... ?
I'd say I care- but I'd probably be lying...
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....
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)....
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
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count!
The O-rings are in a simple stack, the OD is a snug fit in the tube (ie no play).... They are not fastened together in any way, they just sit in a stack up against the back of the valve.... The total valve lift we are dealing with without any buffer is about 0.050"-0.060" at the beginning of the string to 0.100"-0.120" at the end.... When I measured how far the O-ring stack could flex on hammer impact (in this gun), I got about 0.060" for a 4 high stack of 70 Durometer.... and that is with FULL hammer impact, ie after the O-ring stack flexes that far, there is no energy left to open the valve.... In other words, each O-ring distorts from a 0.103" circular cross section to flatten by about 0.015" or so, although the top one may in fact distort more and the one touching the valve less.... I haven't seen any indication that the O-rings are "getting out of place", I would think that would turn up as large jumps in velocity.... I would think that if one got wildly out of place, it would remain so, and turn up on disassembly.... Nor have I heard/read any reports of that happening, although I would agree that is is theoretically possible.... When you go to remove them, you have to hook them and pull them out of the tube....
Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count!
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....
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
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count!
After having a delay due to a burst disc failing and draining my SCUBA tank, and subsequently having to refill it (a long process with a ShoeBox).... I got back to doing more testing today.... I installed a stack of four 90 Durometer O-rings, this time without the 0.055" thick backer ring.... I figured that since the O-rings deflect a lot less than the 70D, I would have sufficient adjustment range between Max. CCW and 4 turns in (the settings I used before) to see what we need to see.... Well, at max. CCW (minimum lift) I got just about what I expected, but the rest of the results leave me totally confused.... Here is what happened....
I used the same colours for all the stroke settings as on the other two graphs.... The vertical scale is the same, but it is shifted down 50 fps in velocity to include all the curves.... The graph is even the same length as the original (no O-ring) graph.... The black "max. stroke" curve starts at nearly maximum velocity, indicating that the hammer spring preload is too high.... The efficiency is 1.23 FPE/CI, in between what I got unbuffered and with the 70D buffer.... I think that if the entire curve was included, it would be a pretty usable string, and the data fits well with what I got using the 70D buffer.... Now for the bad news....
First of all, the other four curves show the OPPOSITE trend for the velocity to what you would expect in a bstaley gun.... As you turn the striker in CW, the valve lift increases, and the velocity is suppose to increase with it.... That was plainly the case with the 70D buffer.... With the 90D O-rings, however, the highest velocity occurred at only 1 turn in, and the velocity DROPPED as I turned the striker in CW, with the lowest velocity (not counting the black line) occurring with the striker in 4 turns.... Three of the curves, on the face of it, look pretty decent in length, 14-15 shots.... The problem is, that the efficiency of all four of these curves was WORSE that the unbuffered gun.... It ran from 0.93 to 1.08 FPE/CI, improving as the velocity dropped.... The velocity with the buffer ran about 30-40 fps lower than the unbuffered gun, and the efficiency was poor as well, so this setup is pretty much a bust, IMO.... The big question is WHY ???
A day or two ago, I had a request to measure the valve lift with a buffer in place.... While I had the stack of four 90D O-rings in the gun, I added the Lift Indicator Rod, set the striker to Max. CCW, readjusted the preload to just shy of cioil bind, and measured the lift at three pressures, 2000, 1500, and 1000 psi.... I then pulled the gun apart, wound the striker in four turns CW, and repeated the measurements.... Here are the results....
A word of caution here.... I was having trouble with the O-ring cocking on the rod (ie not staying perpendicular to it), so it was hard to measure.... I would give a tolerance of about 0.005" plus/minus to the above numbers, but the TREND is pretty clear.... There is VERY little lift occuring when the striker is Max CCW, but it is still about twice as much at 1000 psi as it is at 2000.... and it only takes about 1/64" of lift to produce 640 fps (13 FPE) at 2000 psi.... AMAZING !!! ....
I'll be looking forward to seeing your analysis of these rather confusing results.... So far, it would appear that with a Disco, the 70D O-rings are far superior.... So where do we go from here?....
Bob
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count!
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....
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
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count!
I kinda figured that would occur at some point or another- but I'm not the one doing the testing!
Good luck with the next steps.
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