Inverted BathTub with only 2 bad spots
32 shot string from mostly factory Condor, 24″ barrel .22 cal. shooting Beeman Kodiaks 21.1 grain seated with ball end of Beeman pellet tool.
Fill pressure 2,600 PSI. Top Hat adjusted to 0.085″. POWER wheel set to 1 full turn.
Shot…PSI…….Velocity…..DEViation () indicate negative numbers
3…….2553……971.19…..(16)
4…….2530……922.42…..(65)
5…….2506……987.83…….0
6…….2483……957.29…..(30)
7…….2459……981.19……(6)
8…….2436……989.61…….2
9…….2413……994.98…….8
10…..2389…1,001.23……14
11…..2366……996.45…….9
12…..2342…1,000.99……14
13…..2319……997.19……10
14…..2295……994.33…….7
15…..2272…1,003.39……16
16…..2248…1,004.97……18
17…..2225…1,002.98……16
18…..2202…1,002.23……15
19…..2178…1,002.23……15
20…..2155…1,000.57……13
21…..2131…1,003.97……17
22…..2108…1,004.89……17
23…..2084……999.58……12
24…..2061……994.98…….8
25…..2038……996.29…….9
26…..2014……992.04…….5
27…..1991……983.74……(4)
28…..1967……976.91…..(10)
29…..1944……976.68…..(11)
30…..1920……973.69…..(14)
31…..1897……969.01…..(18)
32…..1873……968.24…..(19)
ENERGY MAX. = 47 foot pounds
Energy Minimun = 40 foot pounds
STANDARD DEVIATION = 17.9 feet per second
My guess is that shots # 4 & 6 were adversely affected by hammer inconsistency. I’m thinking I may need to check the hammer/breech area for burs and maybe get a one piece hammer.
What else could cause such a spur-attic inconsistency?
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That will help as much as anything till you can fill from a quick fill dude…
I have an E-Tac on order my brother.
Sav,
That will help as much as anything till you can fill from a quick fill dude…
Good info Rowdy. I was told that’s why we’re supposed to crank the bleed valve open fast.
So, the proof in this pudding is to fill to 2460 and see if 20 shots look just like the heart of the string above. If they do, you’ve got a perfectly tuned rifle and you’ll have to buy a new one to fiddle with! 😆
Or, you can change the objective to more shots or higher power and still have something to enjoy working on…. 😉
Guys,
My thoughts on the odd shots and how things just don’t always tract the same has to do with two things. One being the hammer bounce and how from one shot to the next we get different readings… Sure some hammers can sit differently in the cocked position making a big difference in how it strikes the valve…
The other is how the amount of bounce we get on the valve and some being enough so that it will purge the valve a little totally wasting the air when it does so… Then this bounce and purge will have the valve seat all set differently and make the next shot different from its amount of energy it takes to open the valve from a bounce/purge… Make sense???
It takes very little difference to change the shot energy on these rifles as you can see when you take your tank off to refill and have the next few shots foul shots from the refill… This is because how the refill has the valve open while it fills the tank and then when we get through filling we allow the seat to close off so much easier than a hard hit from the hammer…
You don’t think so, take the burst disc out of the valve body and screw in a quick fill there, or better yet get the EtaC that Jim has and fill from there and see how much different the shot is from filling like this. Sure its different but nothing as drastic as fill from the stem of the valve… All this gets the difference from how hard or soft the valve is seated… This changes the valves ability to be opened the next shot…
Guys, there is a host of things going on here that all affect each other and the rilfes ability to repeat itself better each shot… Like the valve bounce, you open the valve more by setting the top hat wider, will cause the bounce to be bigger and more often… The hammer and its spring, the valve seat material, the material the hammer is made of, the breech itself and so on and on…
The regulator I want to see if I can get Jim to help me build into his EtaC will help some for sure, but you will still need to work on your setup of each rifle to get this all set better to a relaxed position so that one firing cycle doesn’t generate to much energy and the end result being a bounce cycle that actually opens the valve and purges the tank down an empty barrel… Its just my take on this from when I got my Condor and totally having to rebuild every part on her, with the exception of the frame anyway LOL…
I have limited my weird shots the most so far by adjusting my top hat as close as I have it right now. The least amount you can get the top hat adjusted and still get your FPE, the better you will be… Yes this means you may be limited even more, at least till you get a better valve design…
The prechamber I want to build into the regulator that will be inside the tank will play big roles into all this FPE… We just need to refine these rifles a little more…
Ok thanks. I’m familiar with bell curve. Now I know “bathtub” too.
A Bell Curve 😀 (I prefer bathtub, describes the string better!)
Savagesam,
If you Graph the data you will see the performance improve or decline with each consecutive shot. Some of the experts on the forum have posted pictures of there graphs. A good shot string with our PCP rifles will look like an upside down bathtub starting with a rapid rise in fps followed by a long string of fairly consistent readings and ending with a rapid decline if fps.
Savagesam,
Thanks for asking. I built up a Spread Sheet program that I use as a Master copy, renaming and saving with a new name before I screw up the Master Copy, then I enter the known data. I enter the beginning PSI and the ending PSI and the formulas that I built into the Master Copy fills in the average drop. It may not be perfect readings for each shot but it is a good indication and helps me determine at what pressure things are happening. I had to write in the deviation formula also because I use MS Works and it doesn’t have the deviation formula we need. I enjoy watching the deviation change as I enter the fps. Also, I can delete any bad readings from the mix and make it look better but that’s not reality.
Also, what do you mean by inverted bath tub?
X2
Even with my blod valve/hammer/spring every now and then it’ll throw up an odd number like that. Shoot through a few more strings to see if its an ongoing problem…..
Jerry,
It was 32F, partly cloudy and I was using the cloud screens but the chrony seemed to be working good. When it gives bad readings there are usually several really really bad like in the 4-5,000s. I’m thinking the 2 part AF hammer may be getting repositioned with hammer slap and causing intermittent drag.
Pab,
Sounds like a good plan. I’ve been trying different PSI and finally arrived at the 2,600 psi for this TH setting. I think it’s the first time I’ve seen the rise in fps.
Lurker, Thanks for posting. How are you able to know the pressure all the time? That’s GREAT info.
X2
Even with my blod valve/hammer/spring every now and then it’ll throw up an odd number like that. Shoot through a few more strings to see if its an ongoing problem…..
That’s a reall nice string right there. You may be right in that the hammer didn’t slide right for those two shots but it could also be chrony error. Does it have off shots a lot? I would have expected more “off” shots if you had a significant problem with the hammer.
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never thought to open bleed valve fast , i will try this.
When i am serious about groups i have a sighter target next to my group target, so that when i top off tank after 2- 5 shot groups , i take shots on the slighter target until gun settles in, then go to grouping shots.
I need a e tac too , but when i get one i will have to get a hose, bleed valve , new gauge which i need anyway because the air force gauge on the quick fill sucks,and female quick connect.