Baseline shot string

[dcmeyer]

This is my first shot string from my Hatsan Flash .25

The only things that have been done are a thorough cleaning when new and a couple hundred shots before I shot this.

Started with a 200 bar fill, ended up around 110 bar at the end. There was a slight upward POI change in the middle around 150 bar.

JSB King 25.39
avg 787
es 67
highest fpe at 816 was 37.54

This is my first chrono and string I have done with a PCP. I would appreciate any advise as far as tuning from where it is now. I would like to get to 850fps with these pellets. All I am considering at this point is adjustments and maybe polishing until it's really broken in more.

From what I see it looks better than other Hatsans that have more of a cliff out of the box. Am I correct that if I want to see the full potential fps that I need to increase the hammer spring?

Thank you, but now I have some pumping to do 

[rsterne]

You have about 24 shots within a 4% ES, (816 x 0.96 = 783 fps)…. If you want to keep all your shots within that 4%, and maximize the FPE, you can increase the hammer spring preload so that the first shot at 200 bar is within 4% of the fastest shot in the string.... Of course the entire string will move up in velocity when you do that, and you will likely lose total shot count as well.... You might end up with something like 816-850-816, or maybe even a bit higher velocity.... but 20 shots or less within a 4% ES....

Bob

[dcmeyer]

Thank you Bob.

I don't see any Hatsans in your list but can you recommend increments for adjustment? 1/4, 1/2, full turn at a time? It's just that I'm still hand pumping for now 

[rsterne]

Crank in (out?) about 3 turns and see what you get, and post that.... It seems like you are a fair ways from a 200 bar - 4% ES tune.... I had an AT44 in .25 cal, tuned it for 70 FPE w/ 34 gr. and gave it to my son....

Bob

[dcmeyer]

I believe it is CCW on the Flash to increase but I will re-read some info before I adjust, again, thanks! I will post when I get another string done.

[rsterne]

The AT44 is CCW to increase preload, don't know about the Flash....

Bob

[dcmeyer]

All I can say is, wow! I guess 850fps was a conservative goal.

I went a little more conservative than you suggested, 2 turns CCW. Air consumption is definitely more. From 200 bar to about 110 bar again but with only 30 shots, didn't pick up 2 shots but I think the battery in the chrono is too low on power, it wasn't new, I robbed it from something else because I have everything BUT a 9v around.

JSB King 25.39
avg 843
es 97 - likely took to many shots
highest fpe at 875 was 43.16 - nice!

Should I consider lightening it up a bit for a better shot count? Either way I'm happy, it's making good power which is the goal.

[rsterne]

Using a 4% ES, with an 875 fps peak, you can stop shooting at 96% of that, which is 840 fps.... That would give you 16 shots with that tune.... This string peaks at about 180 bar, the first one at about 150 bar.... Both curves seem to be showing a useful pressure range of about 60 bar.... If that also applies to your final tune, you want it to peak at about 170 bar (start at 200, end at 140)…. I would suggest you back off the preload 1/2 turn, that should put you close for a 200 bar fill....

Let's say when you back the preload down 1/2 turn the velocity peaks at 860 fps.... 96% of that is 825 fps, so you are looking for the string to start at 825-830 fps at 200 bar.... and then stop shooting when it drops back to 825.... I'm guessing you should get pretty close to 20 usable shots within that 4% ES.... It might take you one more 1/4 turn adjustment or less to fine tune it perfectly....

Bob

[dcmeyer]

I see the light enough that I can optimize it from here. Thanks again!

[dcmeyer]

So..... Bob, you are good! Everything positive said here about your knowledge of airguns, and I imagine lot's of other things is likely fact.

You nailed it pretty much spot on from start to finish, here it is with the 1/2 turn back. There were actually 27 shots in this string, shots 5 & 15 were missed in by the chrono and adding those in would have given 23 shots starting from 825 up and back down to 824 with 15 of them over 40fpe. Also had I stopped at the 20 shots the pressure was EXACTLY 140 bar, and would also help the ES and SD numbers.

This must be old hat to you but I am Impressed, and very thankful for your time.

JSB King 25.39

[dlee]

dc- I count 15 full turns between the lowest hammer spring pretension and the highest. Actually abut 15 1/4 to go from hard stop to hard stop. Mine is currently set at 5 turns CCW. With the screw turned all the way clockwise you are at the lowest pretension (it's the opposite of my Urban, for example). You can see from the attached graph that we aren't that far off from one another. I'm getting 27 shots within 4% of max FPS (845fps max). Shooting 25.4gr AA Diabolo Fields. Pstart 200 bar, Pstop 120 bar. Within 35 yds or so, I can basically use all 35 shots for pesting.

[Buldawg76]

Its true that the spring adjuster does travel a total of 15 turns from full CW to full CCW, but the gun will not cock after only 8 turns CCW from full CW so the last 7 turns are not usable. So only 8 turns of adjustment for the hammer spring is useable.

Mine is at 5 turns CCW from full CW and its shooting 720 to 750 and back to 720 for 25 shots with JSB 33.95 grainer using a fill off 200 bar to 120 bar for right at 39/40 FPE per shot. I am happy with that tune for now since I ran out of 25.4s during tuning so swapped to the 33.95s.

Created: 08/07/18 06:14 PM
Description: Flash full power tune
Notes 1: 200 bar start  120 bar end
Notes 2: 5 turns CCW
Distance to Chrono(FT): 1.00
Ballistic Coefficient: 0.036
Bullet Weight(gr): 33.95
Temp: 88 °F
BP: 29.26 inHg
Altitude: 684.00
#          FPS   FT-LBS       PF
29    711      38.11    24.14   
28    718      38.87    24.38   
27    721      39.19    24.48   
26    722      39.30    24.51   
25    732      40.40    24.85   
24    736      40.84    24.99   
23    737      40.95    25.02   
22    742      41.51    25.19   
21    748      42.19    25.39   
20    748      42.19    25.39   
19    751      42.52    25.50   
18    746      41.96    25.33   
17    749      42.30    25.43   
16    744      41.74    25.26   
15    747      42.07    25.36   
14    745      41.85    25.29   
13    741      41.40    25.16   
12    742      41.51    25.19   
11    729      40.07    24.75   
10    742      41.51    25.19   
9     742      41.51    25.19   
8     739      41.18    25.09   
7     734      40.62    24.92   
6     713      38.33    24.21   
5     722      39.30    24.51   
4     720      39.09    24.44   
3     710      38.01    24.10   
2     707      37.69    24.00   
1     701      37.05    23.80   
Average: 732.4 FPS
SD: 14.6 FPS
Min: 701 FPS
Max: 751 FPS
Spread: 50 FPS
Shot/sec: 0.1
True MV: 734 FPS
Group Size (in): 0.00

If you throw out shots 1,2,3 and 28,29 you have a 25 shot string.
Mike

[rsterne]

David, with your top velocity being 870, 96% of that is 835 fps.... I use a 4% ES because that pretty much ends up within average groups at 50 yards.... The shots over 835 are shots 2 - 18, which is a total of 19 shots if you add back in shots 5 & 15.... I would leave the adjustment as you have it, and fill a few bar short of 200 to eliminate that first low shot.... or if you are shooting at shorter range (40 yards or less), you can use all 23 shots, they are within an ES of about 5%....

Congrats on a nice tune....

Bob

[dlee]

Hi Bob, thanks for the tip! My top velocity is actually 845, so 96% of that is 811 fps. Shots 7 and 30 were 810, so I figure those are good. I think that means from shot 4 until shot 30, I'm within 4%. That should be 27 shots within 4%.

Also, I read advice you gave in another thread some time ago about not quite filling to the highest allowed pressure but rather just filling to where the shot string will start at 96% of max fps - I've been doing just that, taking my fill to 195 bar to start. It's much easier to keep track of since that's 3 full mags in .25 cal - I empty 3 mags then refill.

Thanks again! I'm really enjoying this gun - got it for $150 as a refurb a few weeks ago. What a steal.

[dlee]

Bob- sorry, just realized dc's first name is David as well. My bad! Anyway, thanks for your advice - it's always helpful to everyone.

[rsterne]

Yep, wrong David.... *LOL*….

Bob

[dcmeyer]

Now that the rifle has somewhat of a tune I think I found a pellet it doesn't like, at least at this power.

JSB king, JSB King Heavy, H&N Baracuda Hunter all group about the same as before but the 20.06gn FTT started opening up at the higher fps. This target was shot at 20 yards but the rifle was zeroed at 40 yards. I knew i needed some hold under, the aim point was the same on all shots at the bottom edge of the circles, they are 1"

The graph is for the bottom row.

[mcoulter]

Great thread.  I have a .177 Flash.  Subscribing  :-)

[dcmeyer]

Well now it's time to push it to 50 yards and beyond to see what it will do. I was thinking before that the JSB king was going to be "the one" but now after tuning the JSB King Heavy and H&N BH are making over 40fpe over all 20 shots and the JSB King are not. Now to see which one groups best at 50 yards. It may be a week or two as $$ is tight and the scope I have on it is not that great and my only other one is a 3-9x40 fixed parallax at 100, besides it shoots too good on the .22wmr it's sitting on to disturb it 

I'm looking at an Athlon 4-16x40 or one of the UTG's, both mildot.

[Rallyshark]

Well now it's time to push it to 50 yards and beyond to see what it will do. I was thinking before that the JSB king was going to be "the one" but now after tuning the JSB King Heavy and H&N BH are making over 40fpe over all 20 shots and the JSB King are not. Now to see which one groups best at 50 yards. It may be a week or two as $$ is tight and the scope I have on it is not that great and my only other one is a 3-9x40 fixed parallax at 100, besides it shoots too good on the .22wmr it's sitting on to disturb it 

I'm looking at an Athlon 4-16x40 or one of the UTG's, both mildot.

It looks like that Barracuda Hunter will make a dang fine hunting pellet for ya!  It is just as accurate as the JSBs, and those BH pack a wallop on the critters