Tale of THREE BRods - .25, .30 and .357 Completed, Page 19 !

[Hobbyman2007]

Find it looks very similar to my bottle disco build in .25 cal pictured below ,the one in my avatar is in .22 .I used a pice of aluminium channel for a chassis ,it protects the regulator and gauge assembly. Because I'm using a QB drop down there are already holes in the block for the barrel band that helped with securing the chassis. The CAF infantry C7 rifle was the first rifle I ever shot so the feel is quite familiar to me ,and it shoulders easy. Not to mention the weight savings from not having a traditional stock.

[rsterne]

Today I made the cheekpiece for the wooden stock....



It is made from a piece of 1-1/4" ABS pipe cut in half and mounted on two short pieces of aluminum tubing.... This stock has a full length groove that is 1.25" in diameter to fit the main tube, that goes all the way to the back.... The pieces of aluminum tubing are mounted in that groove with wood screws, and then the plastic pipe is mounted to the tubing brackets with 6-32 low-profile SHCSs.... This places the top of the cheekpiece the thickness of the tubing (1/8") above the top of the main tube, which is identical to the AR style stock on the "Black" version.... I'm really happy with the cheek weld using that height and medium scope rings.... This completes the work on the wooden stock....

Bob

[oldpro]

Today I made the cheekpiece for the wooden stock....



It is made from a piece of 1-1/4" ABS pipe cut in half and mounted on two short pieces of aluminum tubing.... This stock has a full length groove that is 1.25" in diameter to fit the main tube, that goes all the way to the back.... The pieces of aluminum tubing are mounted in that groove with wood screws, and then the plastic pipe is mounted to the tubing brackets with 6-32 low-profile SHCSs.... This places the top of the cheekpiece the thickness of the tubing (1/8") above the top of the main tube, which is identical to the AR style stock on the "Black" version.... I'm really happy with the cheek weld using that height and medium scope rings.... This completes the work on the wooden stock....

Bob

Now that is Sexy looking

[dud]

Although I don't feel worthy to post on your posts AR stocks are outstanding for fire control, especially when it's time to rock and roll. It's funny when the first m16s where issued they where thought as a BB gun. But marksmanship increased. 

[grand-galop]

Today I made the cheekpiece for the wooden stock....



It is made from a piece of 1-1/4" ABS pipe cut in half and mounted on two short pieces of aluminum tubing.... This stock has a full length groove that is 1.25" in diameter to fit the main tube, that goes all the way to the back.... The pieces of aluminum tubing are mounted in that groove with wood screws, and then the plastic pipe is mounted to the tubing brackets with 6-32 low-profile SHCSs.... This places the top of the cheekpiece the thickness of the tubing (1/8") above the top of the main tube, which is identical to the AR style stock on the "Black" version.... I'm really happy with the cheek weld using that height and medium scope rings.... This completes the work on the wooden stock....

Bob

Do you feel this one to be more balanced in the hand??  Nice piece of art...   

[rsterne]

I haven't assembled the wooden one with a bottle yet, so can't comment on the balance....

After assembling the wood version with the .25 cal barrel and the Cothran valve, I decided to try some of the 41 gr. BBTs that I cast a week ago.... I tried some as cast, and they were a bit tough to load, they were better at 0.254", and at 0.253" you could feel them seat in the chamber, but you didn't have to push very hard.... I will test different diameters for accuracy at a later date, but for now I am using them sized to 0.253" for my Chrony work.... The hammer is the 28 gr. MDS hammer I made with the aluminum core and an adjustable striker.... I tethered the gun at 1900 psi, set the striker flush with the end of the hammer, and set the hammer spring preload to zero, and started testing.... I am still using the same spring, but without the SSG, so that I can adjust the striker through the middle of the spring and rear adjuster bolt....

I checked the velocity first with the 34 gr. JSB King Heavies, and it was 978 fps (73 FPE) as expected at this pressure... The first shots with the BBTs were 918 fps for the 41.7 gr. FN (78 FPE) and 938 fps for the 39.5 gr. HP (77 FPE).... Leaving the striker flush, I backed out the preload a turn with no change, and then 2 turns, and the velocity tanked.... I then turned the preload back in a turn, it was back to normal, and then I backed out the striker 1 turn below flush (recessed into the hammer).... The velocity was normal, so I backed it out another turn, and the gun did not fire.... The hammer is hitting the bumper on the back of the valve, and at this combination of preload and recessed striker, the valve is not opening at all.... I left the striker recessed, and started adding preload to the spring, and by adding a couple of turns I was able to get it to fire weakly.... After some experimenting with different settings, I decided to set the preload 1 turn out from zero (ie a slight gap between the hammer and spring), and to set the striker 1 turn below flush on the face of the hammer.... At this striker setting, the hammer is hitting the bumper when the valve is open about 0.070", and it really won't matter how much preload I add, it won't open further, at least in theory.... I am hoping that when I connect it back up to a bottle so that I can check the efficiency, I will have found an improvement, both from the heavier bullets, and from limiting the valve lift.... which may reduce the dwell slightly....

The experimenting I have done so far with an adjustable striker mirrors what happens with changing the preload.... Basically the valve is either cycling properly, or it isn't and falls off the cliff.... At 1900 psi the velocity with the 34 gr. JSBs is a bit higher than desired at 978 fps.... while these BBTs are a fraction lower than I want.... I would like to see the FN solids at just under 950 fps, and the HPs at just over, for a solid 80 FPE.... I think bumping the pressure to 2000 psi would do the job.... However, to get results I can compare to my previous ones, I will leave the 500 cc bottle regulated at 1800 psi for now.... and connect it back up for some efficiency testing....

Bob

[rsterne]

I did some measurements of the efficiency of the .25 cal version with the Cothran valve today.... I tethered the gun to the 500 cc bottle, with it regulated at 1800 psi, the same as I did previously.... I was using the 28 gram MDS hammer with the aluminum core and adjustable striker, and the same spring but without the SSG in place (so that I can adjust the striker), and the energy absorbing polymer (IsoDamp) bumper on the back of the valve.... With this setup the hammer stops when it hits the valve (bumper), and the amount the valve opens is dictated by the position of the striker, relative to the face of the hammer.... If the striker is flush, the valve can open about 0.108".... if the striker protrudes, it can open further (up to the 0.200" limit of the valve stem protrusion).... and if recessed the valve opens less (recessed 3 turns the valve can't open at all, no matter how much hammer spring you use).... With relatively light preloads, the valve quits opening if the striker is recessed about 2 turns into the hammer face.... ie the gun will not fire at all with the striker recessed more than 2 turns....

As I experiment with the adjustable striker, I am coming to some interesting conclusions about the Cothran Powerhouse valve (whether they are correct or not, I don't know).... I think the valve, once opened a small amount, and with enough backpressure in the exhaust port, "blows open".... From actual lift measurements I made on the Disco version, when cycling properly it opens about 0.060"-0.120".... while when it has fallen "off the cliff" it is opening about 0.020" or less.... Normally, a valve opens pretty much in a linear relationship to the hammer strike, the Cothan does not.... The interesting part is, that with the adjustable striker in this gun, I can get the valve to cycle reliably (providing I have enough hammer strike) with the striker recessed into the hammer face 1.5 turns, which in theory means it can only open the valve about 0.050".... Now perhaps the bumper is compressing, and the valve stem is getting pushed a few thou further, but I don't think there is any way it is getting to 0.060".... and yet the measurements I made with the Disco valve (which is identical inside) say that the valve is opening that far or more.... This has led me to the conclusion (unproven) that once the valve opens about 0.030", it blows open to provide twice that much actual lift.... Right or wrong, that is what I THINK is happening....

Like most valves, if you hit them way too hard, they waste air.... In my first tests with the Cothran valve, whacking it hard didn't produce any more power, but I could make the gun use up to 80 psi per shot, with an efficiency of less than 0.50 FPE/CI.... This is usually an indication that the valve is still open after the pellet has left the muzzle.... As you approached the cliff (from the plateau), the efficiency came up to around 0.65 FPE/CI, and then just before you got to the cliff it increased to just under 1.0 FPE/CI, using about 35-40 psi per shot with the 34 gr. JSB King Heavies.... I was curious what would happen to the efficiency using the adjustable striker to restrict how hard you could hit the valve, regardless of the hammer spring preload.... I wasn't disappointed....

If I set the striker so that it protruded 3 turns from the hammer face (the same thickness as the bumper on the back of the valve), then the bumper never came into play, and the valve acted just like it did before.... Whack it too hard, and the efficiency went into the tank.... When I set the striker flush with the hammer face, however, things changed.... In theory, the valve could only be driven open about half way, and that is exactly the way it acted.... That is far enough to deliver maximum velocity, but not enough to drive the valve so far open that it becomes an air hog.... No matter how much preload I used on the hammer spring, I couldn't get the gun to use more than 40 psi per shot.... Compare this to the 80 psi per shot it would use if you really whacked it before, and you realize that what the bumper does is stop the hammer before it opens the valve further than required, even if you use way too much hammer strike.... It's like having a "limiter" on the amount of air the valve can use.... This is obviously a very good thing, as it makes it extremely easy to not use way too much air.... However, 40 psi per shot is still not great for efficiency, it is only about 0.85 FPE/CI with the 34 gr. JSBs.... It was now time to explore what happened when you tuned closer to the "cliff"....

I now had the ability to approach the cliff in two ways.... I could do it by reducing the preload, or by reducing the initial valve opening, or both.... Believe me, I burned through a lot of pellets and bullets, and a tank of air, trying to figure out what was going on, and which worked better.... I tested with the 34.2 gr. JSB King Heavies, the 39.5 gr. NOE HPs, and the 41.7 gr. NOE FN.... Both the BBTs were sized to 0.253".... I determined that I could recess the striker as much as 1.5 turns into the hammer face and still have the valve cycle properly.... I tried various preloads with it set there, and with it set flush (and in between), and determined that all that happened was it took a slightly different amount of preload to reach the cliff, and the psi of air used for an 8-shot magazine didn't really change.... It was how far from the cliff you were that determined how much air you used.... However, I reasoned that the less lift I allowed with the striker (while still having enough to cycle the valve), the less sensitive the preload might be, and the less difference it would make in air usage if you used too much.... In reality, I don't think it mattered much, but I got some pretty decent efficiency numbers while operating in the 71-75 FPE power range....

Something else I discovered is that the BBTs used less air than the pellets.... I don't know if that is because they were tighter in the bore, heavier, and therefore building more backpressure, causing the valve to close faster, or some other effect.... but instead of 320 psi for 8 shots, they only used 280 psi.... and this was when operating up on the plateau, well above the cliff.... Since I was also getting 2-3 more FPE with the BBTs, this put their efficiency at over 1.0 FPE/CI, instead of under with the pellets.... As I backed off on the preload and approached the cliff, the pressure drop for 8 shots dropped to 270 psi for the pellets and 240 psi for the BBTs, while the velocity only fell off 2-3 fps.... There was about a 1/2 turn range of preload over which the change in velocity and air use was slight, making it much easier to tune just above the cliff, but with consistent velocity.... Here are the final results at 1800 psi....

JSB 34.2 gr.... 969 fps.... 71.3 FPE.... 1.00 FPE/CI
BBT 39.5 gr. HP.... 918 fps.... 73.9 FPE.... 1.17 FPE/CI
BBT 41.6 gr. FN.... 898 fps.... 74.7 FPE.... 1.18 FPE/CI

With the BBTs, I was getting a pressure drop on the 500 cc bottle of 240 psi for 8 shots.... With the regulator set at 1800 psi, that should work out to about 5 magazines (40 shots) at 75 FPE per fill (a total of 3000 FPE).... or about 35 shots with the JSBs at 71 FPE.... I am beginning to think that the Cothran valve is better suited to bullets than pellets.... and quite likely the heavier the better.... If I were tuning for the 34 gr. JSBs, I would probably reduce the setpoint to 1700 psi for 70 FPE.... while for the BBTs I would increase it to 2000 psi, where it should be a good, solid 80 FPE gun.... with a low ES and a decent shot count....

One thing for sure, anyone using a Cothran valve in an MRod might like to consider putting a couple of # 118 O-rings inside the tube, right up against the back of the valve (assuming a stock hammer with flanged, adjustable striker).... If you are using a hammer with a flush face, like the new WAR MDS hammer, a single one should prevent you from opening the valve so far that it will waste a ton of air.... If the valve is capable of opening 0.090" or so, it never needs to open more than that, from what I have seen.... The stem protrudes just under 0.200", so with an O-ring being 0.103" thick, and a flat faced hammer, you should never have to worry about opening the valve too far and dumping air after Elvis has left the building.... Playing with the preload to get close to the cliff and optimize the efficiency is all that would be left to do, once you get the pressure set to give the velocity you want with the pellet you are using....

Bob

[grand-galop]

WOW!!  Nicely done Bob...  Back pressure is the added ingrediant that need to be add to the mix..  Gotcha!!

[oldpro]

 This is exactly what Ive seen also Bob as the bullet weight goes up the efficiency gos up and this can be contributed to the poppet return orifice in the stem. Inside the poppet stem is a sliding metering rod that acts like a valve. Once high pressure air is introduced into said orifice it blows by metering rod and slams it closed thus preventing the back pressure from getting out then the trapped air forces the poppet closed. Now Don never intended the valve to be used in the manner in which we are trying to use it so POWER is what he was after and using a lot of air to get there. So the more back pressure (heavier bullet) you can produce the faster the valve shuts. So what Im doing literally right now is opening up that tiny .015 hole to .030 to introduce more back pressure and with a heavier return spring also I expect(hope) we will see a much more efficient valve for small bores. Don has been working with me every day and and having him on the team is awesome and having Bob answer my silly questions has saved me so much R&D time.  We will get there Im sure of it.     

[rsterne]

The backpressure acts in a strange way.... Without it, the valve won't cycle properly.... If you shoot a PCP with a Cothran valve in it, without a pellet, the valve doesn't open properly.... It needs that pressure in the exhaust port to open fully.... and then also uses it, flowing through that tiny vent hole, past the metering rod in the stem, to close again.... At least I think that's how it works.... *LOL*.... You can prove this to yourself by adjusting it to open properly, but near the cliff, with a bullet.... and then try a lighter pellet, and the valve barely opens....

I have a slightly different take on the efficiency.... I think the valve, at a given pressure, wants to release a certain amount of air, or saying it another way, stay open for a set amount of time.... If the dwell is a constant, the heavier bullet has moved less down the bore in the time the valve is open, releasing a smaller quantity of air (the lower psi drop I saw with a heavy bullet).... Now that air has more distance to expand in, creating slightly more FPE.... Less CI of air, creating more FPE, means a higher FPE/CI.... ie higher efficiency....

Bob

[oldpro]

 Ok just got done with first string after drilling stem hole and this should be proof enough. I drilled it to .030. Thats and avg FPE/cuin per shot of 1.63 BY FAR the best I have had from the warp at this power level BUT some draw backs, it now closes fast and chops the power and needs higher reg pressure to get to previous power levels. Higher reg pressure leaves less head room but the report from gun is acceptable again!!! More testing to do.     
Description: Warp 30
Notes 1: 3k 2200psi
Notes 2: Mod DC valve
Distance to Chrono(FT): 1.00
Ballistic Coefficient: 1.000
Bullet Weight(gr): 50.00
Temp: N/A °F
BP: N/A inHg
Altitude: 0.00
#          FPS   FT-LBS       PF
20    692      53.17    34.60   
19    694      53.48    34.70   
18    688      52.56    34.40   
17    701      54.57    35.05   
16    700      54.41    35.00   
15    693      53.33    34.65   
14    706      55.35    35.30   
13    684      51.95    34.20   
12    702      54.72    35.10   
11    702      54.72    35.10   
10    703      54.88    35.15   
9     702      54.72    35.10   
8     703      54.88    35.15   
7     709      55.82    35.45   
6     710      55.98    35.50   
5     714      56.61    35.70   
4     709      55.82    35.45   
3     717      57.09    35.85   
2     723      58.04    36.15   
1     713      56.45    35.65   
Average: 703.2 FPS
SD: 9.9 FPS
Min: 684 FPS
Max: 723 FPS
Spread: 39 FPS
Shot/sec: 0.0
True MV: 703 FPS
Group Size (in): 0.00

[rsterne]

Sounds like you have drastically reduced the dwell by drilling out the vent hole.... Problem is, it's a one-way street, go too far, and you need a new poppet.... I wonder if sanding down the metering rod would give you more control, and if you go too far, you just make a new one from a piece of 1/8" drill rod.... I guess it will depend on which is the restriction, the vent hole or the annular space around the metering rod....

Having to increase the pressure to get back to the same FPE sounds indeed like you have shortened the lift and/or dwell.... With the valve closing earlier in the shot cycle, you are releasing less air during the open cycle, and that air has more distance in the barrel to expand, helping get back some of the lost FPE, and increasing the efficiency.... It makes perfect sense, now all we need is to find a way to make that venting, and therefore the dwell, ADJUSTABLE.... 

I know you are using a stiffer valve spring, did you try the original spring with the drilled out vent hole?.... could be you could drop the pressure again?....

Bob

[oldpro]

Sounds like you have drastically reduced the dwell by drilling out the vent hole.... Problem is, it's a one-way street, go too far, and you need a new poppet.... I wonder if sanding down the metering rod would give you more control, and if you go too far, you just make a new one from a piece of 1/8" drill rod.... I guess it will depend on which is the restriction, the vent hole or the annular space around the metering rod....

Having to increase the pressure to get back to the same FPE sounds indeed like you have shortened the lift and/or dwell.... With the valve closing earlier in the shot cycle, you are releasing less air during the open cycle, and that air has more distance in the barrel to expand, helping get back some of the lost FPE, and increasing the efficiency.... It makes perfect sense, now all we need is to find a way to make that venting, and therefore the dwell, ADJUSTABLE.... 

I know you are using a stiffer valve spring, did you try the original spring with the drilled out vent hole?.... could be you could drop the pressure again?....

Bob

First thing tomorrow ill be putting back Dons stock return spring as like you said and I thought it  may gain back the FPS and leave more head room and still allow for better efficiency. What Don and I are trying to do is make the valve more flexible across the spectrum. So hes willing to make changes to the valve as needed. Tomorrow Ill have more testing to do but i see the light at the end of thr tunnel. And on changing the metering rod well i did that and it caused all kinds of problems but ill call you tomorrow and explain.

[lloyd-ss]

Bob,
I have experienced exactly the same results when adjusting the hammer strike and hammer spring preload that you are describing in reply#166.
My setup uses the same IsoDamp that I gave you, a stock spring, and an adjustable striker.  The cross over point for opening the valve is a delicate balance, but after reaching that cliff, the valve seems to open fully all by itself.  I was using a hammer of about 50 grams. I finally arrived at a spring preload of only .18" and a valve stem strike distance of only .027".  In other words, the striker drove the valve stem only .027" before the hammer was stopped by the IsoDamp.  The striker might have traveled a few thou more, but still, the amount that the stem needs to be "pushed" is minuscule.  My gun uses a 20" barrel, and I found that even doubling the hammer preload and/or doubling the striker travel made almost no difference in power, but it did seem to use more air. 
It was very interesting that when the preload and striker were adjusted to just barely fully open the valve, that shortening the striker distance by only .009", or decreasing the spring preload by only .015" would reduce the velocity by 400 fps, almost cutting the velocity in half.
Lloyd

[rsterne]

Nice to see your comments, Lloyd, I miss your input when you are busy with other things.... I agree that when you are on the cliff (falling over it), the velocity changes very rapidly with miniscule changes in preload or striker distance.... However, if it was just a matter of it being sensitive, I could live with that, and just figure out how to make tiny adjustments.... The problem is, that with the valve being so sensitive between 400-900 fps (ie while dropping off the cliff), I find the velocity to be totally inconsistent.... You can shoot 5 shots, and have two "normal" shots of over 900 fps, and the other three anywhere between 400-700 fps.... I have literally seen an ES of 500 fps within 5 shots.... This, of course, is totally unacceptable.... so I see little choice but to run the valve solidly on the plateau, but as close to the edge of the cliff as possible without falling over it....

Bob

[oldpro]

Nice to see your comments, Lloyd, I miss your input when you are busy with other things.... I agree that when you are on the cliff (falling over it), the velocity changes very rapidly with miniscule changes in preload or striker distance.... However, if it was just a matter of it being sensitive, I could live with that, and just figure out how to make tiny adjustments.... The problem is, that with the valve being so sensitive between 400-900 fps (ie while dropping off the cliff), I find the velocity to be totally inconsistent.... You can shoot 5 shots, and have two "normal" shots of over 900 fps, and the other three anywhere between 400-700 fps.... I have literally seen an ES of 500 fps within 5 shots.... This, of course, is totally unacceptable.... so I see little choice but to run the valve solidly on the plateau, but as close to the edge of the cliff as possible without falling over it....

Bob

I agree with this and making any FPE/FPS changes requires adjustment of pressure valve sees and just leave valve on the knee. The regulator is now your hammer spring adjustment per say as well as T-port changes to add or subtract back pressure to close valve. I find it much easier to find the knee using a limiter for valve over travel just like you and Bob have both done and using reg pressure to then get me to desired FPE. 

[rsterne]

OK, I think I am FINALLY beginning to understand how the Cothran valve reacts to different setups and calibers.... I replaced the .25 cal upper with the .30 cal upper today, with NO other changes.... It was still tethered to the 500 cc tank with a regulated output of 1800 psi, and the striker is still set at 1.5 turns below flush on the hammer.... This means it drives the valve open about 0.050", although it may blow open further than that if it wants to.... I initially used the same 2 turns of gap between the spring and the hammer that I started with yesterday, loaded a magazine up with 7 of the JSB 50.2 gr. pellets, and fired a shot across the Chrony.... about 400 fps.... OK, I half expected it would need a harder hammer hit with the larger bore, so I added a turn of preload.... 930 fps.... GREAT, so now I know that there is hardly any difference in how hard you need to hit the valve with a .30 cal compared to a .25 cal.... That is quite different than a conventional valve, which usually requires a significantly harder hammer strike as you increase the caliber, to fill the larger barrel volume....

I topped up the 500 cc tank, leaving my Great White tethered to it with the valve closed, so that I could use the big gauge to read the pressure drop in the 500 cc (same as I have been doing with all these tests), shot a couple of shots to stabilize everything, recorded the pressure, cranked in 8 turns of preload, and shot a 7 shot mag. across the Chrony and recorded the new pressure.... It dropped 380 psi.... Bear in mind that similar tests without the striker recessed showed as much as 80 psi pressure drop per shot, so the recessed striker certainly saves a lot of air if you have wayyyyyyyyy too much hammer strike.... I backed the preload off to 4 turns, the velocity dropped only 3 fps, and the pressure drop for 7 shots was 300 psi.... I then set the preload to zero, still the same velocity and pressure drop, so the gun was acting exactly the same as it did yesterday with the .25 cal barrel on it, at the same settings.... even the same pressure drop, although this was for 7 shots (at 97 FPE) instead of 8 shots (at 71 FPE).... I then backed the preload out another turn (1 turn of gap, now), lost another 2 fps, but the pressure drop was now only 280 psi.... One more turn out (which worked fine with the .25 cal), and I was back down to ~400 fps, so I added 1/2 turn, and the valve was back to cycling solidly and reliably, at 926 fps (96 FPE), with only a 240 psi pressure drop for 7 shots.... This works out to 1.33 FPE/CI, a very respectable efficiency for a .30 cal gun at this power level.... I only needed 1/2 turn more preload in .30 cal than I did in .25 cal....

So to summarize, when set about 1/2 turn of preload above the cliff, so that the valve cycles solidly, reliably, and with low ES (well under 1%), and shooting pellets.... I am getting 8 shots in .25 cal at 71 FPE on 280 psi of air (1.00 FPE/CI).... and 7 shots in .30 cal at 96 FPE on 240 psi of air (1.33 FPE/CI).... In my Disco Double, at the same pressure, in .357 cal, I was getting 128 FPE at 1.53 FPE/CI (78 gr. pellets @ 862 fps).... I think it is pretty clear what is happening here.... The Cothran valve, when cycling properly but operating just above the cliff.... has a relative constant dwell, so providing the barrel is long enough that the valve is closing well before the pellet reaches the muzzle, it is dumping a relatively constant amount of air into the barrel.... Yes, it dumps a bit more into a larger bore, but relative to the bore volume, it is less, which means the valve is closing sooner in the larger caliber, leading to higher efficiency.... This behaviour also explains why we were getting such high FPE/CI numbers in .357 cal but pretty miserable numbers in .25 cal. and the .30 cal is right in between....

This leads me to a pretty obvious conclusion.... The Cothran valve is a way better choice for larger calibers and heavier bullets.... ie for high FPE applications.... However, as we gain a better understanding of it, we can tame it down for use in regulated PCPs as low as .25 cal....

Bob

[lloyd-ss]

Bob,
I have observed the same phenomenon and definitely tend to agree with your conclusion. 
I have also observed some super sensitivity in the distance that the striker drives the valve stem. For instance, (as in reply #173 above) when the spring and striker were set to barely, but fully, open the valve, turning the striker in 1/4 additional turn (.009) required that the spring ALSO be turned in by a larger amount, approx .025", to keep the valve opening fully.  I don't really understand why it seemed to take disproportionate amount of additional spring preload  to compensate for the increase in striker travel. A mystery.
Lloyd

[Motorhead]

The AREA of a hole .015" and that of .030" is HUGELY different !!!
Frankly would have taken .005" or LESS incremental size enlargement steps to get a more definitive cause & effect graphed out.

JMO ....
Scotty

[rsterne]

I suggested the same thing to Travis, Scott.... I would start at stock (0.020") and go 0.002" at a time and graph out the results.... keep going until you either hit a straight line plateau, or the velocity was so low as to be useless....

Bob