2400kt, Bottled, Regulated

[nervoustrigger]

Wow, amazing that web of material held together as long as it did!   Definitely a good candidate for a high durometer replacement.

Regarding the extrusion versus heat failure, I want to stress that was just my experience.  You clearly can distinguish the differences so you are in a good position to deal with whatever curveball your particular pump throws your way.

[aPpYe]

Yeah, i wamted to replace it with a high durometer ring, but the local hardware store (I am about fifteen minutes from a small mountain town and the nearest city, Fresno, is an hour away) only had orings in the plumbing section, so it is most likely another 55d  buna-n once again.  I am sureni will be replacing it again... What can I say?  I am impatient and wanna shoot my gun NOW! I am also guilty of jackhammering as you put it.  Lots of fills from empty during (at least in theory!) the early stages of owning my first PCP, degassing, pulling it apart, etc... 

After I got it back together, I tried the idea of "boosting" the pump with my shop compressor on the inlet. I have now filled a couple times this in this fashion, and its nice to be able to pump the gun up in so few strokes.  I can imagine this being even harder on the rings... There was already a leak at the base of the of the pump from the moment I hooked the compressor to it, as that ring is compression set pretty badly.   I am really gonna have to fashion some bigger dessicant filters, especially if I am gonna continue to do the shop compressor thing, as my little harbor freight filter is most likely still letting some moisture through.  Speaking of which, it is about time to get those beads into the oven...

[aPpYe]

Hi All,

I guess a clean barrel really DOES matter ... lol.  Anyway, after fiddling with everything else, I found I got nice tight ES's when I mounted the 10" barrel from my 1377.  I figured that before I wrote it off, I would really try and do a thorough cleaning of the 24" barrel.  I grabbed my bore snake that I use on my .22lr barrels, cut the weight off, loaded it with brake cleaner and ran it through about ten times, soaking it through a few times in between.  It was VERY hard to pull through!  After I was done bore snaking, I noticed that the crown looked like it had some sort of "mushrooming" nicks on the end, like the extra material had been pushed out from inside of the barrel.  I don't know if this was because I used a .22lr bore snake on a soft .177 airgun barrel, or due to the fact that the barrel was filthy, but I went ahead and recrowned once again using the brass screw method.

After putting everything together once again, I found that my tight ES's were once again back!  Perhaps not to their former >10fps consistency, but I was able to consistently achieve about 10-20fps ES across 10 shots, depending on the pellet.  This is at least acceptable to me.  Accuracy does not seem to have been adversely affected by running the larger bore snake ... I am still able to pretty much stack pellets at ~20yds, and am able to stay sub 1" at 50 yards.  This is good enough for me, as those groups are achieved bag rested and with a scope, but the gun will spend most of its time with a peep sight, hiking along my local hills with me, bouncing pebbles around at 30 yards or so.  I have yet to actually kill anything with this gun, so I am getting a little bloodthirsty.  Squirrels or rabbits will be this thing's main prey I think.  I am confident I can easily drop something like that out to 70 yards or so if I am at full power with the heavies...

I have made a promise to myself to NOT disassemble this gun again until at least the beginning of March!

Efficiency per shot on PCPs tends to go up with pressure, for a given FPE.... In a regulated PCP, however, the "headroom", or the difference between your fill pressure and setpoint pressure goes down, reducing the overall amount of air you have available.... Finding the best balance between the two will give you the most shots at a given FPE.... As you reduce the pressure (like aPpYe is doing), you will eventually get to the point that you cannot get the FPE you want, or you will be operating up on the plateau of the curve where the efficiency is terrible.... and even though you have more headroom (air) available, your shot count will drop.... This has nothing to do with SSGs, of course....

Bob, I once again want to apologize for almost derailing your SSG thread.  I wasn't paying attention to what I was doing.  Anyway, I am not really sure how all this works with the SSG now in the mix.  I was thinking that so long as I am at or below the knee, then the lower I can take the pressure the more shots I would get per fill.  More headroom as you say...  Currently, I am running at ~850fps with the 10.34gr heavies.   With the SSG installed, and the RVA turned all the way in, this is the maximum velocity the gun will achieve.  With the SSG removed, maximum velocity is around 885-890fps or so.  I am not sure why this discrepancy exists... Interestingly, the SSG installed, I am at ~850fps, from 0-2 turns out on the RVA, and at 2.5 turns, the velocity is around 820 or so.

Anyway, wouldn't this still be considered an "efficient" setup?

[rsterne]

It sounds like from 0-2 turns out with the SSG (at 850) you are on the plateau with that setup, and you have no gap.... You are only getting a decrease in velocity at 2.5 turns out, which is when the gap is starting.... If you want more velocity, you will either need more pressure, or a longer, softer spring on the SSG with more preload to get the hammer energy back up to what it was without the SSG....

I can't comment on the efficiency without hard numbers as to total FPE and total air used....

Bob

[aPpYe]

Okay, hard numbers this time.  I ran out of jsb heavies, so I had to wait for new ones to arrive.  Being without decent pellets is PROBABLY not as bad as being without heroin, but I tell you it isn't fun!

All better now.

First, I shot these groups.  The "Description" field shows the amount of turns out:

Set: 1
Created: 02/13/16 08:36 AM
Description: 0 Turns
Notes 1:
Notes 2:
Distance to Chrono(FT): 1.50
Ballistic Coefficient: 0.031
Bullet Weight(gr): 10.34
Temp: 44 °F
BP: 30.25 inHg
#          FPS  FT-LBS      PF
5    859      16.94    8.88
4    875      17.58    9.05
3    868      17.30    8.98
2    881      17.82    9.11
1    865      17.18    8.94
Average: 869.6 FPS
SD: 8.6 FPS
Min: 859 FPS
Max: 881 FPS
Spread: 22 FPS
Shot/sec: 0.1
True MV: 873 FPS
Group Size (in): 0.00

--------------------------------------------
Set: 2
Created: 02/13/16 08:39 AM
Description: 1 Turn
Notes 1:
Notes 2:
Distance to Chrono(FT): 1.50
Ballistic Coefficient: 0.031
Bullet Weight(gr): 10.34
Temp: 44 °F
BP: 30.25 inHg
#          FPS  FT-LBS      PF
5    854      16.75    8.83
4    875      17.58    9.05
3    874      17.54    9.04
2    865      17.18    8.94
1    860      16.98    8.89
Average: 865.6 FPS
SD: 9.0 FPS
Min: 854 FPS
Max: 875 FPS
Spread: 21 FPS
Shot/sec: 0.1
True MV: 869 FPS
Group Size (in): 0.00

--------------------------------------------
Set: 3
Created: 02/13/16 08:41 AM
Description: 2 Turn
Notes 1:
Notes 2:
Distance to Chrono(FT): 1.50
Ballistic Coefficient: 0.031
Bullet Weight(gr): 10.34
Temp: 44 °F
BP: 30.25 inHg
#          FPS  FT-LBS      PF
5    823      15.55    8.51
4    836      16.05    8.64
3    840      16.20    8.69
2    827      15.71    8.55
1    830      15.82    8.58
Average: 831.2 FPS
SD: 6.8 FPS
Min: 823 FPS
Max: 840 FPS
Spread: 17 FPS
Shot/sec: 0.1
True MV: 834 FPS
Group Size (in): 0.00

--------------------------------------------
Set: 4
Created: 02/13/16 08:43 AM
Description: 1.5 Turn
Notes 1:
Notes 2:
Distance to Chrono(FT): 1.50
Ballistic Coefficient: 0.031
Bullet Weight(gr): 10.34
Temp: 44 °F
BP: 30.25 inHg
#          FPS  FT-LBS      PF
6    844      16.36    8.73
5    867      17.26    8.96
4    862      17.06    8.91
3    860      16.98    8.89
2    849      16.55    8.78
1    ERROR 2
Average: 856.4 FPS
SD: 9.6 FPS
Min: 844 FPS
Max: 867 FPS
Spread: 23 FPS
Shot/sec: 0.1
True MV: 860 FPS
Group Size (in): 0.00

--------------------------------------------


As you can see, the velocity doesn't really drop off until about 1.5 - 2 turns out.  At ZERO turns out, there is definitely a gap between the striker and the SSG.  It is approximately 3/4 of the width of the hammer pin...  Anyway, some hours later, I shot this string:

Created: 02/13/16 11:12 AM
Description: 1.5 EFFICIENCY
Notes 1:
Notes 2:
Distance to Chrono(FT): 1.50
Ballistic Coefficient: 0.031
Bullet Weight(gr): 10.34
Temp: 56 °F
BP: 30.26 inHg
#          FPS  FT-LBS      PF
61    845      16.40    8.74
60    844      16.36    8.73
59    850      16.59    8.79
58    845      16.40    8.74
57    ERROR 3
56    852      16.67    8.81
55    853      16.71    8.82
54    852      16.67    8.81
53    856      16.83    8.85
52    ERROR 3
51    851      16.63    8.80
50    845      16.40    8.74
49    852      16.67    8.81
48    853      16.71    8.82
47    850      16.59    8.79
46    855      16.79    8.84
45    856      16.83    8.85
44    843      16.32    8.72
43    854      16.75    8.83
42    851      16.63    8.80
41    848      16.51    8.77
40    846      16.44    8.75
39    849      16.55    8.78
38    848      16.51    8.77
37    848      16.51    8.77
36    846      16.44    8.75
35    853      16.71    8.82
34    848      16.51    8.77
33    853      16.71    8.82
32    846      16.44    8.75
31    861      17.02    8.90
30    850      16.59    8.79
29    853      16.71    8.82
28    ERROR 10
27    850      16.59    8.79
26    851      16.63    8.80
25    851      16.63    8.80
24    856      16.83    8.85
23    ERROR 3
22    854      16.75    8.83
21    855      16.79    8.84
20    858      16.90    8.87
19    850      16.59    8.79
18    ERROR 3
17    849      16.55    8.78
16    849      16.55    8.78
15    849      16.55    8.78
14    852      16.67    8.81
13    847      16.47    8.76
12    858      16.90    8.87
11    855      16.79    8.84
10    852      16.67    8.81
9    853      16.71    8.82
8    856      16.83    8.85
7    853      16.71    8.82
6    849      16.55    8.78
5    851      16.63    8.80
4    861      17.02    8.90
3    851      16.63    8.80
2    858      16.90    8.87
1    859      16.94    8.88
Average: 851.5 FPS
SD: 4.2 FPS
Min: 843 FPS
Max: 861 FPS
Spread: 18 FPS
Shot/sec: 0.0
True MV: 855 FPS
Group Size (in): 0.00

This string consumed exactly 1000psi of air, going from 3000psi - 2000psi (according to the rather low resolution ninja regulator's gauge) ... So with an average of 851.5fps (16.65fpe):

     (16.65 x 61) / 1000 = 1.01565 fpe/psi ... This is the correct formula, right?

I would think I could clear 120+ shots per fill with the current 1050-1100psi set pressure, but I was hoping I would see the 1.5ish fpe/psi I see people reporting in the SSG thread...  Would a higher set point likely yield better efficiency?

[rsterne]

You don't measure FPE/PSI, as it doesn't take into account the volume of the air reservoir.... I would be OK for your gun, but you can't compare to others.... To calculate the total volume of air used (at 1 bar), you multiply the pressure drop (1000 psi) by the reservoir volume in cu.in. (If you are using a 13 CI tank, multiply by 13) and then divide by 14.5 (psi per bar).... If you are using a 13 CI tank, that works out to (1000 x 13 / 14.5) = 897 CI of air used.... The total FPE is the average times the number of shots, so 16.65 x 61 = 1016 FPE.... The efficiency is the total FPE divided by the total air volume used to produce it.... (1016 / 897) = 1.13 FPE/CI.... If your tank is not a 13 CI tank, that number will be incorrect, of course....

A higher setpoint will yield a higher efficiency.... but if you go very far and then detune back to the velocity you have now, the velocity will INCREASE below the setpoint.... 1100 psi should be close for the FPE you have now.... 

Bob

[aPpYe]

Lol on missing the volume of air, I don't know how many times have seen fpe/ci (never fpe/psi!) mentioned...  Schoolboy error.   Amateurism on public display!  Thanks for taking the time to explain.

I am curious to see if I can achieve higher efficiency at a higher psi and knee...  1200psi should bring the knee to 900fps.

You know, just as I came to start getting a handle on this tuning thing, your SSG came along sent my head spinning!  I should double check, but the knee should be at the same velocity with/without SSG, right?  It seems I am reaching a knee now, as velocity out to 1.5 turns barely drops...

[rsterne]

It is possible that the SSG introduces a "false knee" if you plot velocity vs gap.... This is because as soon as you create a gap (for most SSG types) the velocity starts to drop off immediately as you increase the gap.... This does NOT happen on some types of SSGs, the velocity stays quite constant over the first turn or so (what you are experiencing), and that could be because you are on the plateau if you had no SSG in place.... or it could be some other factor.... At least one SSG design shows a slight INCREASE in velocity until the gap is about 0.020-0.040", and then a rapid decline.... I think the increase is because in that SSG type, where the hammer has to accelerate the guide at contact, and it is actually the end of the guide that opens the valve.... it takes a small amount of movement after first contact to get the guide moving at full speed....

The point is, that an SSG could well mask where the knee of the curve is, because it is not a linear device like a simple hammer spring.... This is obvious when you set one to have even slight preload instead of a gap.... the gun gets LOUD and uses a ton more air, as if you turned on a switch.... and when you back it out again to create the gap, the gun gets much quieter and uses a lot less air as soon as the gap appears.... To determine if you are still on the plateau or the downslope, you need to see what happens as you increase the preload (with no gap).... If the velocity continues to increase, you are on the downslope.... If it holds steady, you are on the plateau.... Since I tune my guns for the "knee", I increase the preload on the SSG until I no longer see a velocity increase.... Then when I back off the SSS to create a gap, as soon as I start to see the velocity decrease, I know I am on the knee of the curve.... If you can turn your SSG out 1.5 turns before the velocity drops, I would suggest that is where the knee STARTS.... From zero gap to 1.5 turns out, you are likely on the plateau.... If you need more velocity, your only solution (unless you hog out the ports) is more pressure....

Bob

[aPpYe]

Since I tune my guns for the "knee", I increase the preload on the SSG until I no longer see a velocity increase.... Then when I back off the SSS to create a gap, as soon as I start to see the velocity decrease, I know I am on the knee of the curve.... If you can turn your SSG out 1.5 turns before the velocity drops, I would suggest that is where the knee STARTS.... From zero gap to 1.5 turns out, you are likely on the plateau.... If you need more velocity, your only solution (unless you hog out the ports) is more pressure....

Hmm.  I am thinking that I need to thread another SSG.  I do not have a lathe, only a rotary tool, a drill press and a bench grinder.  For this reason, and the fact that there really isn't any danger of pinching on a 2400kt, I am still using the original SSG design.  I have a TON of preload on my spring right now though.  I think I tuned backwards.  I already cut off the excess threads from the end of the one I have now, so I cannot back off preload any further. 

You have once again powered a light bulb in my head.  Looking at the photos of the first SSG you posted in your thread, I am assuming that is what it looked like tuned to the knee.  The RVA looks to be turned out at least several turns already.  Now, my understanding of tuning with an SSG (assuming I am looking for the "knee") is as such:

• Without the SSG installed, or at least with the stopping nut(s) and o-ring removed, and using a chronograph, determine the maximum average velocity (at least 5 shots) of a pellet at a given regulator set point.
• Install the SSG guide shaft into the gun and back the RVA out as far as possible.
  
  • In my case, this is about 14.5 turns.  The Challenger RVA (with the degasser tool threads drilled out to allow for the 3/16 SSG guide) stops engaging the spring at about 14.5 turns, but can't be removed until over 20 turns ... The spring rests against the internal threads of the end cap after 14.5 turns.
• Install the stop nut and o-ring on the guide shaft, turning the nut in until the o-ring is lightly sandwiched between the surface of the RVA and the nut.
• Determine velocity over 1-2 shots.
• Increase preload by turning the stopping screw in a fraction of a turn.
• Maintain zero gap by also turning the RVA in the same distance.
  • I am assuming we want zero gap here, maybe even put a little load on the valve spring?  I am winging it here...
• Determine the new, higher velocity over 1-2 shots.
• Repeat steps 5-7 until the AVERAGE velocity in step 1 is achieved.
  • I stress average velocity here to avoid misreads.  Until we get close, it isn't really necessary to get an average, right?
• Introduce a gap (0.020"-0.040") by backing off the RVA.
• Determine average velocity.
  
  • If average velocity remains the same after introducing the gap, increase gap until velocity falls into the knee of the curve.
  • If average velocity drops immediately, slightly increase preload on the spring until velocity does not drop with a gap of 0.020"-0.040"
• Any further velocity adjustments, say for lighter pellets or 5fpe indoor shooting should be done by increasing the gap with the RVA.

Does this all sound right?  It does to me, though it wouldn't be the first time my logic was based on notions that get me so far out in left field I don't even realize my own team is at bat.  Currently, there is a LOT of preload on on my spring.  I was more concerned with making sure that I could still cock the gun with the RVA at 0 turns.  It seems I should abandon that notion.  If I don't like how far my RVA is sticking out of the rear, I can always cut a few threads off and readjust...

I don't expect this procedure it to make any difference to efficiency, but it would make for easier cocking, although I don't consider it to be difficult to cock now...  I will also make sure to leave an inch or so of threads on the end of the guide shaft before increasing pressure.  Once I am happy with things, I can cut off the excess again.

Since I am going to be tracking down the check engine light on my jeep today, I am looking at doing this tonight or tomorrow evening...

As far as getting more velocity, I am not really after that so much as I want to see if I can get better efficiency while staying on the knee of the curve.  It would be interesting to see if I can get that number to climb when I am shooting from a 900fps knee...  I also remember you mentioning at one point that enlarging ports and whatnot isn't really the way to go with .177, as it can actually decrease efficiency...

What would be a realistic goal for maximum efficiency (at the knee) for a 24" 2400kt in .177 with 10.34 JSB heavies?  I want to keep knee velocity well under transsonic turbulence, so I don't really want to shoot much higher than 925fps.  I know I can get the knee to that velocity with a 1400psi set point.  I don't mind the ~850fps I am at now, but I would like to achieve something better than 1.13fpe/ci at the knee if I can...  Lower velocities and lighter pellets are secondary concerns, and I understand that these velocities will increase below the set point if I am shooting on the downslope rather than the knee...  When I am shooting at 5fpe indoors, I am fine with that.  At those power levels, shot counts before even getting close to set pressure is ridiculously high anyway...

[rsterne]

Your tuning method should work.... I likely use fewer preload changes.... Note, I am nearly always tuning for the "knee" of the curve, with the ability to go lower by increasing the gap.... This requires I know where the knee is, before I start working on an SSG for that gun.... so I have a target for my maximum velocity....

1. Determine maximum velocity without SSG, ie where the "plateau" is for the pellet/barrel/pressure/porting combination you have.... and what the velocity is on the "knee" of the curve.... That will be your goal for the SSG with a small, but workable gap, where it is preventing hammer bounce as it should....
2. Try and figure a rough idea of the AVEARAGE cocking force as set up above....
3. Select a spring that when set up with preload of 4-5 lbs. (typical) will have an average cocking force the same or greater, and hopefully with a lower maximum cocking force....
4. Make a spring guide of the correct length to give you about 2-3 lbs. of preload, with enough adjustment (or the potential for adjustment) to exceed 5 lbs....
5. With the preload set as in #4, install the SSG and adjust to "no" gap.... The velocity will almost certainly be below maximum.... Confirm by adding some preload with the gap adjuster.... The report, and velocity, should increase....
6. Increase the preload on the spring guide at least 1 turn (I typically use 0.1" increments).... About 1 lb. more preload per step would be a good choice....
7. Set to no gap, check velocity.... Add some preload / negative gap - you should notice a large increase in the report, and some extra velocity.... Back off to 0.020-0.040" gap and record velocity....
8. Repeat steps 6 & 7 until you can achieve, or nearly achieve, your maximum velocity when preload (ie no gap) is present....
9. Set the gap to minimum, record the velocity, increase the gap in small increments, and record it again.... I like to see the velocity "just tickling" the plateau with no gap....
10. Check your efficiency and velocity with various gaps, and determine what adjustment meets your requirements....

If at any stage along the way you hit coil bind, you need a longer, softer spring, and more room for it behind the hammer.... The above is just one way of tuning an SSG....

Bob

[aPpYe]

Hi Bob,

It seems I am on the right track then!  All right!  I am officially calling myself "intermediately skilled" ... no longer a newbie!

Anyway, it seems I was editing my post while you replied to it.  I will quote myself below ...

What would be a realistic goal for maximum efficiency (at the knee) for a 24" 2400kt in .177 with 10.34 JSB heavies?  I want to keep knee velocity well under transsonic turbulence, so I don't really want to shoot much higher than 925fps.  I know I can get the knee to that velocity with a 1400psi set point.  I don't mind the ~850fps I am at now, but I would like to achieve something better than 1.13fpe/ci at the knee if I can...  Lower velocities and lighter pellets are secondary concerns, and I understand that these velocities will increase below the set point if I am shooting on the downslope rather than the knee...  When I am shooting at 5fpe indoors, I am fine with that.  At those power levels, shot counts before even getting close to set pressure is ridiculously high anyway...

[rsterne]

All I can suggest is trying different combinations of preload and spring length.... It sounds like you are pretty close to the plateau with your current setup, that may be the reason you can't improve your efficiency without further reducing the velocity.... More pressure may be required....

Bob

[aPpYe]

1.48404154 fpe/ci!!!

I'm just gonna say it:

     BITCHIN!!!

Okay, now that we have that out of the way, going up to 1200-1250psi (set point range) really made a difference!  With the SSG uninstalled (or with just the stop nut removed, it didn't make any discernable difference), the plateau is at about 920fps with JSB Heavies.  I think the highest was 926fps.  Anyway, the maximum velocity I could achieve with zero gap was about 900fps.  Once I introduce gap, the velocity starts to fall right away, as suggested before.  Now, with the velocity adjuster turned all the way in, and with about .02" gap (between 3-4 flats on a 10-24 nut), I am averaging 884.8fps, which should put me in the well into the knee.  I will report later on which way the spread goes below set pressure...  Anyway, I shot a string from 3000psi to 2500psi, stats as follows:



Average: 884.8 FPS
SD: 4.9 FPS
Min: 874 FPS
Max: 894 FPS
Spread: 20 FPS
True MV: 885 FPS

This was looking PESSIMISTICALLY at the pressure gauge.  I likely could have included another 3-5 shots in the string ...

I am not sure what "True MV" is, and I am still trying to wrap my head around standard deviation...

Anyway, if I am using your formula correctly, I used 448.275862ci of air, achieving a total of 665.26fpe, so 665.26/448.275862=1.48404154 fpe/ci!  I may try 1400psi at some later date, but so far I am extremely happy with this vast improvement!  These are the numbers I was hoping for when I first saw the SSG!

And yeah! I made a chart!  Bob, what application are you using to make yours?  It took me a few minutes to figure it out in libreoffice, but it still doesn't look as cool as the ones you make...

[nervoustrigger]

Efficiency of 1.5 in .22 cal at over 30fpe.   Well done, sir!

[aPpYe]

Huh?   No this is .177 at about 18fpe...   JSB Heavy 10.34gr!

[nervoustrigger]

Oops, sorry!  I was looking at it quickly on my phone.  That being the case, it's no less impressive in my book.

[rsterne]

I use Excel for my spreadsheets and charts.... and CONGRATS, BTW !!!

Bob

[aPpYe]

Thanks again for the tech support, all!

Here is a string I shot yesterday when I noticed that my pressure was at around 1400psi...



I would call shot #7 a fluke, I am not sure what is going on with the spike after shot #21, and shot #25 didn't register on the chronograph.

If I remember right, with the shims set up as they are now, the regulator outputs ~1200psi when the bottle is at 1500psi, and at 1250psi when the bottle has 3000psi.  These readings were taken from the benjamin hand pump, the ninja bottle gauge, and a separate, larger 3000psi gauge I bought to test regulator output pressure.   Below set pressure, all three gauges seemed to agree with one another quite closely.  Above set pressure, the bottle and pump seem to agree pretty consistently all the way up to 3000psi.

So I started at ~1400psi.  It was at about 1250psi at shot 12 or so.  Again, this is looking at the low resolution ninja gauge, so it's hard to tell for sure ... I guess I am splitting hairs at this point, but with the dropoff being so gradual after that, this should put me right at the sweet spot of the knee, right?  Of course, this is just one string ... 

There is that little spike after shot 21, but I was well under set point by then, so I don't think that is indicative of being on the downslope... I would be comfortable shooting down to 1000psi with this setup, at least offhand.  Staying above set point, I should have a total shot count (18fpe) of around 130 per fill.  Not bad!

[nervoustrigger]

Getting over a ton (literally) of energy from a 13ci tank is a fine result.  Superbly done!

[rsterne]

Unfortunately, I think you are confusing "knee" and "downslope" with the shape of your shot curve, those terms have nothing to do with the velocity plot in your last post.... They mean how the velocity relates to the hammer spring preload AT CONSTANT PRESSURE....

If you think that your setpoint pressure was reached at around shots 12-15, since I see no sign of a slight increase in velocity at that point, that would indicate you are likely operating on, or close to, the plateau of the curve at 1200 psi.... If you were on the downslope, the velocity would increase dramatically below the setpoint.... If on the knee, it should increase very slightly, or the shot string should at least extend below the setpoint for a few shot before the velocity drops off....

Bob