Tuned AT44 Long (.177) Shot String

[SpiralGroove]

Hey Scott,
Did you mean lower the set-point a tad?
Kirk

[Motorhead]

Hey Scott,
Did you mean lower the set-point a tad?
Kirk

No ... you read right

[stretch]

I would love to get 64 good shots on a single cylinder.  Thanks very much for sharing this!

[rsterne]

Kirk, I think you should take a bow!.... You've stuck with it until you got what you wanted.... I think that's a really good result.... I know that you are on the knee of the curve from the velocity vs. hammer preload numbers you sent me in PM, so if you make any further changes they will have to be really small, and they may or may not increase your total shot count....

What Scott is saying is that you are still relatively close to the plateau (ie on the high side of the knee), which is why you are not seeing a slight rise in velocity as you come off reg.... If you were down below the knee, on the downslope, you would see that rise, and the further you are down the downslope, the more pronounced it will be.... Scott and I like to tune so that when you get to the setpoint, you see just a slight rise (no more than 1%) and then a gradual fall off.... That extends your shot count BELOW the setpoint pressure 100-200 psi.... To get there from where you are now, just to see what will happen, screw in (reduce) the preload a turn, you should see what we describe happening (but at a lower velocity)....

To get that type of tune, and not give up any velocity, you have to increase the setpoint slightly.... I'm guessing that you won't have to change the preload, however, as you want to be slightly further down the knee of the (now higher) curve.... It's a toss-up whether or not your total shot count will increase.... You will have less "headroom" (pressure range from full to setpoint), which reduces the shotcount.... However, when you tune it down to your present velocity, at that higher pressure, you will increase the efficiency, slightly, getting some or all of those lost shots back.... Then once you add on being able to shoot down below the (new higher) setpoint, you may well get a few more shots.... If you're not totally exhausted, it's worth a try.... Just make sure you RECORD your current settings in case you have to come back to them....

Bob

[SpiralGroove]

Scott,
I didn't know this would happen; it seems counter intuitive!  -> I didn't begin shooting a PCP rifle until August 2014

So you're saying by increasing the setpoint (a tad) and increasing the hammer strike (slightly), I would actually be increasing the efficiency of the gun to overcome the (seemingly) additional air being used ? (higher fps due to ^ setpoint & ^ hammer strike - should use more air; hence less shots ). 
Are you also suggesting this could help me reach my goal of 70 shots with a higher ES  ?

Sorry, if this is not very fluid.................Kirk

[SpiralGroove]

Preload looks like this:
0 turns = 882 fps
1 turn  = 913 fps **
2 turns = 950 fps
3 turns = 959 fps

** This is where my shot string is..........setpoint 1450 (I think - I increased setpoint  1/8 turn CCW this AM).
Sorry if I'm missing the point............

[rsterne]

I would have thought my explanation before your previous post was pretty clear.... As I  explained, if you reduce your preload to zero, and shoot a string, I would expect you to get about 70 shots at 882 fps, and then a slight rise to less than 900 fps once BELOW the setpoint, and then a fall-off.... Try it and see what you get, no harm, right?....

Bob

[SpiralGroove]

Hey Stretch,
Remember this tune is on the AT44 Long (230cc air cylinder).  I subtracted 45 cc for the regulator & plenum, giving me a total of 185 cc of remaining air.  The AT44 Short (185 cc), subtracting 45cc, gives a remainder of 140 cc or about 50 shots with the above tune.

[SpiralGroove]

Hey Bob,
OK----------> Will try.  Sorry for the occasional Thickheadiness 
My skull is not a permeable membrane for osmosis.............Kirk

[Motorhead]

Kirk,
Not sure what to say ? ... Bob did a great explanation a few posts up on the dynamics of what was suggested.
Your so very close to an optimum setting ... fiddle for perfection or just go shoot it !!

Regards,
Scott

[SpiralGroove]

In the AM, will increase setpoint 1/8 turn CCW & leaving preload at 1  turn out -> and fire away.
Sounds like maybe 70 shots at 2.6% ES is in her yet   If I don't get may 70 shots, will try preload of 0 & 2 or thereabouts
Kirk

[rsterne]

What you are suggesting may well work.... I myself would prefer to change one thing at a time.... You have never, so far (AFAIK) seen that slightly increasing string below the setpoint, which is why I suggested you leave the gun alone except for reducing the preload and see if you can see it.... That will at least show you what Scott and I are talking about.... Assuming it does, then increasing the setpoint slightly and leaving the hammer strike alone will likely put you very close to your goal....

It's kind of teaching a guy how to fish, instead of giving him a fish.... for me, anyway....

Bob

[Motorhead]

It's kind of teaching a guy how to fish, instead of giving him a fish.... for me, anyway....

Bob

A very good analogy there Bob ... agree   

[SpiralGroove]

Thank God I love to fish, especially Large Mouth Bass

[SpiralGroove]

Hey Bob & Scott, since this is pretty much a conversation between us, you're right, methods aren't very systematic, as I often try multiple changes at once (my bad).

After increasing the setpoint 1/8 turn (CCW) I ran the following preload test.
0 turns out   649, 652, 658, 664
1 turn out    728, 721, 725, 733
2 turns out   813, 837, 840, 846
3 turns out   916, 926, 916, 935
4 turns out   970, 982, 986, 989
My regulator seems to be having problems

Shot String: 3 - 1/4 turns out (200 bar to 100 bar)  This one is bazaar?

   1-10   876, 884, 903, 897, 915, 914, 908, 927, 921, 935
 11-20   925, 929, 940, 950, 954, 963, 947, 950, 953, 964
 21-30   957, 966, 984, 966, 973, 988, 976, 976, 988, 991
 31-40   969, 979, 988, 988, 996, 974, 988, 982, 973, 984
 41-50   992, 994, 957, 966, 934, 944, 949, 943, 942, 929
 51-60   917, 928, 921, 910, 900, 908, 903, 893, 888, 881

Comments:
1) Now this almost looks like an unregulated string!
2) ES is wretched
3) The gun is more efficient than before to get than many high FPS shots.
4) Will likely pull regulator & check for damages (I've had to pound it "in & out" a few times).  The lock washer had been slipping before.  Will take apart and make sure all o-rings are in place, check delrin seat and lock washer. 
It's been abused more than you guys
5) Preload needs to be reduced to 3 or 2-3/4 turns out.
Kirk
     

[rsterne]

Seems to me that something went south on you before you ran this test.... I would agree that the string looks unregulated, and your preload tests confirm that, look at the low velocity at 1 turn out compared to before you reset the reg.... you lost ~ 200 fps with only 1/8 turn?.... I would say the reg. is bypassing....

Bob

[SpiralGroove]

OK Guys............I've had enough of this tune

Got some decent results when I increased the setpoint 1/8 turn more CCW, however, the regulator's ES went through the roof.  Started at 907 and went to 950 off the regulator.  Finally decided to overhaul the regulator and re-lube; lowered setpoint slightly-> close to where it was on my last posted string (here).  Pleased with the ES of the string, but not my shot count goal.  I may try one more string with 3/4 turn out , but will not bore you with it.  Anyway...........

String:
   1-10   914, 915, 912, 913, 916, 917, 917, 922, 915, 920
  11-20  911, 920, 922, 915, 900, 920, 915, 917, 913, 915 
 21-30   916, 915, 915, 910, 919, 918, 916, 916, 910, 915
 31-40   911, 918, 910, 913, 910, 913, 916, 917, 920, 910
 41-50   911, 916, 920, ER2, 907, 909, 904, 910, 916, 912
 51-60   916, 915, 916, 916, 909, 919, 906, 904, 900, 908
 61-70   900, 903, 895, 884 880 
60 shots from 200 bar to 100 bar, E=1.07, ES=2.4%, CPUM, 1 turn out. 

[rsterne]

I still suggest you try a string at zero preload and look for that slight rise in velocity below the setpoint.... I think this is the best string you have done so far....

Bo

[SpiralGroove]

Hey Guys,
For target pratice, my best two strings were:
1) 80 shots using CPUM, setpoint 1450, 200 bar to 80 bar, 0 Preload turnouts, Ave. 890 fps, E=1.21% ES First 70 shots 2.4%
2) 70 shots using CPUM, setpoint 1550, 200 bar to 100 bar, 1 preload turnout, Ave 901 fps, E=1.17%, ES=2.6%
Kirk

[rsterne]

I think you're there!.... Congrats !!!

Bob