Huben GK1 .25 tuning for Altaros & JSB - charts and data

[JDGriz]

I've compiled some chronograph data for the GK1 V3 in .25, with Altaros 50gr slugs. One of the data columns is with 51gr slugs, because I ran out of 50s (they are smooth-walled and this might be reducing the power by 2-3 fpe, looking at the data).
Unscrewing the power screw all the way until it starts to rotate freely (and no more than this) is the position of maximum power. Screwing it in, clockwise, from that position, takes 3.5 revolutions until its all the way in - this is the lowest possible power.
I've done six tests, all labeled by their number of turns/revolutions, clockwise, from the position of maximum power. For example, "1.125 Rev. CW" means turning the power screw clockwise one full turn, then another 45 degrees. "1.25 Rev. CW" is one full turn then 90 degrees more. "1.5 Rev. CW" is one and a half turns.
I tested the pistol gauge accuracy by attaching an inline digital gauge while filling. The digital gauge read "350 bar" when the pistol gauge was at 355 bar - so good enough for testing; the data uses the readings of the pistol gauge as it was.

It is unlikely that this data would be too relevant with other pellets/slug weights and the exact number of turns might vary a bit between individual pistols.

This is the data in chart and table forms:

0.0 Rev. CW 50gr
bar fps fpe
1 350 891 88
2 330 868 84
3 310 848 80
4 290 828 76
5 265 798 71
6 240 770 66
7 225 753 63

0.5 Rev. CW 50gr
bar fps fpe
1 355 893 89
2 333 870 84
3 315 855 81
4 295 837 78
5 280 819 74
6 263 802 71
7 247 782 68
8 233 766 65
9 217 745 62
10 205 727 59
11 193 706 55
12 188 687 52
13 165 662 49
14 153 659 48
15 137 605 41

1.0 Rev. CW 50gr
bar fps fpe
1 347 847 80
2 335 839 78
3 320 832 77
4 307 827 76
5 295 819 74
6 284 813 73
7 270 802 71
8 258 793 70
9 248 781 68
10 236 767 65
11 225 754 63
12 213 743 61
13 203 725 58
14 193 709 56
15 185 695 54
16 175 678 51
17 165 658 48

1.125 Rev. CW 51gr
bar fps fpe
1 355 824 77
2 340 803 73
3 328 796 72
4 316 801 73
5 303 797 72
6 290 793 71
7 278 788 70
8 267 781 69
9 255 768 67
10 242 754 64
11 232 740 62
12 220 726 60
13 210 709 57
14 197 693 54
15 187 678 52
16 180 661 49
17 168 644 47

1.25 Rev. CW 50gr
bar fps fpe
1 350 773 66
2 335 758 64
3 323 748 62
4 314 751 63
5 305 752 63
6 295 753 63
7 285 757 64
8 274 758 64
9 264 765 65
10 255 763 65
11 245 763 65
12 237 756 63
13 227 748 62
14 218 738 60
15 208 727 59
16 198 715 57
17 190 703 55

1.5 Rev. CW 50gr
bar fps fpe
1 353 699 54
2 343 685 52
3 335 684 52
4 325 679 51
5 318 681 52
6 312 681 52
7 305 682 52
8 295 683 52
9 288 686 52
10 282 691 53
11 273 693 53
12 265 696 54
13 257 698 54
14 248 701 55
15 242 706 55
16 235 705 55
17 228 711 56
18 220 716 57
19 215 713 56
20 207 710 56
21 198 704 55
22 192 696 54
23 185 686 52
24 177 674 50

 

[MrP]

Who was it who was insisting there would never be a string at 60 FPE for this pistol .

 

[JDGriz]

It's a bit slow though. I wonder if lead-free Altaros-shaped slugs woudn't be a good idea; good ballistic coefficient _and_ good speed. Or to drill a hole in the back of the lead 50 grainers. Or is that not how ballistic coefficients work (?).
There are many other slug/pellet options with higher speeds (in the 30-40 grain range), but none of those have as good BCs - 35 gr might be optimal.

 

[silvershooter589]

Beautifully charted data and impressive results!

 

[Bernie7]

Excellent contribution to the community

Also why did you stop shooting on the 0 revolutions (max power) after 7 shots, looks like there was still plenty of air in the tank?

 

[Nomadic Pirate 66]

Jeez, look at those last 2 strings...amazing,
and then look at the first 2 strings......90 FPE with a pocket pistol ? that is absolutely crazy.

What a wonderful piece of kit this Huben pistol is.

Yeah I think 35-40gr ammo is a better choice for the pistol, I might order some 38gr NSA one day.

 

[JDGriz]

Also why did you stop shooting on the 0 revolutions (max power) after 7 shots, looks like there was still plenty of air in the tank?

The first two settings (0 and 0.5 Rev) are wasting air; the valve might still be open after the projectile has left the barrel. It is more noticeable on a chart of FPS vs. shot number.

 

[longdog]

Received my .25 from Kelly(what a pleasure to deal with) yesterday.
Installed a 2-7 Hawke on BKL mount last nite.
The gun was filled to 32.5bar as received.
Trigger was too light(got a couple of “double shots“, so I turned the left adjustment screw CW about 3/4 turn. This adjustment gave me a near perfect trigger pull …..no more double shots.
The power as received was about 450fps so closed the power adjuster and opened it 2 turns CCW. This gave me 795fps with 25.39gr Kings.
Topped it off with 32.5bar which gave me 2 magazines(34 shots) to 17bar. FPS was 798 to 783 over 34 shots.
Here’s the accuracy results after sight in at 27yrds.
39 degrees with zero wind.
To say that I’m pleased is an understatement.
Absolutely amazing guns!

I meant this to be posted in the “Huben Pistol” thread but don’t no how to change it…..can the mods move it please.

 

[JDGriz]

..More charts and data, for JSB .25, 25.4gr, same procedure.
It looks like the flattest setting would be around 750-770 FPS.

0.5 Rev CW
no. Bar FPS FPE
1 345 1027 59.5
2 333 1016 58.2
3 320 1015 58.1
4 310 1014 58.0
5 302 1006 57.1
6 290 1001 56.5
7 278 997 56.1
8 268 988 55.0
9 258 975 53.6
10 247 961 52.1
11 235 950 50.9
12 223 936 49.4
13 210 917 47.4
14 197 900 45.7
15 185 875 43.2
16 173 855 41.2
17 163 834 39.2

1.0 Rev CW
no. Bar FPS FPE
1 345 950 50.9
2 333 940 49.8
3 325 932 49.0
4 317 924 48.1
5 310 920 47.7
6 300 924 48.1
7 290 918 47.5
8 284 919 47.6
9 275 922 47.9
10 267 918 47.5
11 260 920 47.7
12 251 921 47.8
13 243 917 47.4
14 237 914 47.1
15 230 911 46.8
16 223 912 46.9
17 216 911 46.8
18 210 897 45.4
19 205 892 44.9
20 197 885 44.2
21 188 876 43.3
22 181 865 42.2
23 175 852 40.9
24 167 836 39.4
25 161 827 38.6

1.5 Rev CW
no. Bar FPS FPE
1 345 820 37.9
2 337 820 37.9
3 328 819 37.8
4 323 821 38.0
5 317 820 37.9
6 310 816 37.5
7 303 816 37.5
8 298 818 37.7
9 291 817 37.6
10 286 818 37.7
11 278 814 37.4
12 273 817 37.6
13 267 819 37.8
14 262 820 37.9
15 256 821 38.0
16 251 822 38.1
17 245 826 38.5
18 240 832 39.0
19 233 833 39.1
20 228 831 38.9
21 222 835 39.3
22 217 840 39.8
23 212 846 40.4
24 207 849 40.6
25 202 853 41.0
26 196 855 41.2
27 190 854 41.1
28 185 853 41.0
29 180 851 40.8
30 174 841 39.9
31 168 834 39.2
32 163 823 38.2
33 156 812 37.2
34 153 800 36.1

2.0 Rev CW
no. Bar FPS FPE
1 340 704 27.9
2 335 699 27.6
3 330 701 27.7
4 325 696 27.3
5 320 698 27.5
6 316 695 27.2
7 312 697 27.4
8 308 698 27.5
9 304 693 27.1
10 300 692 27.0
11 296 686 26.5
12 291 696 27.3
13 287 689 26.8
14 283 688 26.7
15 279 686 26.5
16 275 684 26.4
17 273 682 26.2
18 268 682 26.2
19 265 683 26.3
20 260 684 26.4
21 255 677 25.8
22 252 680 26.1
23 248 680 26.1
24 245 682 26.2
25 242 680 26.1
26 238 680 26.1
27 235 675 25.7
28 232 678 25.9
29 228 674 25.6
30 225 677 25.8
31 222 676 25.8
32 219 680 26.1
33 215 675 25.7
34 212 674 25.6
35 209 672 25.5
36 205 671 25.4
37 202 670 25.3
38 200 666 25.0
39 196 664 24.9
40 193 656 24.3
41 190 665 24.9
42 187 669 25.2
43 185 671 25.4
44 182 671 25.4
45 180 671 25.4
46 177 677 25.8
47 174 676 25.8
48 170 682 26.2
49 167 682 26.2
50 165 680 26.1
51 162 684 26.4
52 159 688 26.7
53 157 695 27.2

2.5 Rev CW
Shot No. Bar FPS
1 345 579 18.9
2 340 573 18.5
3 335 570 18.3
4 328 567 18.1
5 325 568 18.2
6 325 565 18.0
7 320 567 18.1
8 318 562 17.8
9 315 565 18.0
10 313 563 17.9
11 310 560 17.7
12 307 560 17.7
13 304 560 17.7
14 302 561 17.7
15 300 561 17.7
16 298 559 17.6
17 293 560 17.7
18 290 557 17.5
19 286 558 17.6
20 285 557 17.5
21 283 556 17.4
22 278 559 17.6
23 275 559 17.6
24 273 559 17.6
25 270 557 17.5
26 267 557 17.5
27 264 556 17.4
28 261 557 17.5
29 259 555 17.4
30 256 556 17.4
31 254 555 17.4
32 252 557 17.5
33 249 554 17.3
34 245 550 17.1
35 240 551 17.1
36 240 550 17.1
37 238 550 17.1
38 235 548 16.9
39 232 548 16.9
40 230 548 16.9
41 228 545 16.7
42 225 546 16.8
43 224 547 16.9
44 221 543 16.6
45 219 544 16.7
46 216 542 16.6
47 215 544 16.7
48 213 538 16.3
49 210 540 16.4
50 210 538 16.3
51 205 537 16.3
52 203 535 16.1
53 200 534 16.1
54 199 536 16.2
55 197 533 16.0
56 195 534 16.1
57 192 533 16.0
58 190 531 15.9
59 190 531 15.9
60 188 529 15.8
61 186 529 15.8
62 185 527 15.7
63 183 526 15.6
64 181 528 15.7
65 180 527 15.7
66 178 526 15.6
67 175 521 15.3
68 171 521 15.3
69 170 520 15.2
70 167 523 15.4
71 165 525 15.5
72 165 517 15.1
73 163 519 15.2
74 163 520 15.2

 

[weevil]

JD - very nice - many thanks. I would propose that a second flat string would be a setting that gives 850fps at full fill, given that all of the higher power setting strings coalesce to that speed at ~170bar. Somewhere between orange and grey. I guess there’s a point at which all these strings meet, at an unusably low pressure. Visible for the Altaros and hinted at by the increase at the lower end of yellow in this data. Very interesting dynamics and clearly different from a hammered unregulated PCP. Really shows the value of investigation to optimize settings and run with a speed that the system, with a given projectile, favors. I wish I could fill to 350 but I’m a tank user.

Obviously, this is a great weight of projectile for use in 25.

 

[JDGriz]

JD - very nice - many thanks. I would propose that a second flat string would be a setting that gives 850fps at full fill, given that all of the higher power setting strings coalesce to that speed at ~170bar. Somewhere between orange and grey.

Yes! I missed that one.

I guess there’s a point at which all these strings meet, at an unusably low pressure. Visible for the Altaros and hinted at by the increase at the lower end of yellow in this data.

The tangent line is where the valve is open all the way until the projectile leaves the barrel (and more). At higher power settings this happens at higher pressures.

 

[Asher]

JD - very nice - many thanks. I would propose that a second flat string would be a setting that gives 850fps at full fill, given that all of the higher power setting strings coalesce to that speed at ~170bar. Somewhere between orange and grey. I guess there’s a point at which all these strings meet, at an unusably low pressure. Visible for the Altaros and hinted at by the increase at the lower end of yellow in this data. Very interesting dynamics and clearly different from a hammered unregulated PCP. Really shows the value of investigation to optimize settings and run with a speed that the system, with a given projectile, favors. I wish I could fill to 350 but I’m a tank user.

Obviously, this is a great weight of projectile for use in 25.

I just recently got a cs4 otherwise I'd be stuck with just a tank too (and my huben hand pump i suppose, but that thing takes like 150 strokes to fill the pistol) and would not get quite as much enjoyment out of the gk1.

 

[JDGriz]

This is the JSB .25 MK2 data and charts (33.95 gr). I think there might be two power settings that might work better than the rest across the board - "1.25 Rev" and "1.75 Rev"

0.5 Rev CW
no. Bar FPS FPE
1 340 972 71.2
2 325 963 69.9
3 313 955 68.8
4 302 945 67.3
5 288 933 65.6
6 274 919 63.7
7 259 903 61.5
8 245 888 59.5
9 230 872 57.3
10 218 852 54.7
11 205 833 52.3
12 192 814 50.0
13 182 791 47.2
14 170 774 45.2
15 158 747 42.1
16 145 721 39.2
17 130 691 36.0

1.0 Rev CW
no. Bar FPS FPE
1 350 898 60.8
2 335 878 58.1
3 323 869 56.9
4 315 873 57.5
5 307 865 56.4
6 299 861 55.9
7 290 866 56.5
8 280 871 57.2
9 270 872 57.3
10 262 868 56.8
11 253 873 57.5
12 245 869 56.9
13 236 864 56.3
14 227 857 55.4
15 218 841 53.3
16 209 828 51.7
17 199 815 50.1
18 189 805 48.9
19 180 790 47.1
20 172 775 45.3
21 165 758 43.3
22 155 739 41.2
23 146 723 39.4

1.25 Rev CW
no. Bar FPS FPE
1 349 832 52.2
2 339 819 50.6
3 329 822 50.9
4 321 822 50.9
5 314 820 50.7
6 305 820 50.7
7 298 818 50.5
8 290 822 50.9
9 283 831 52.1
10 275 836 52.7
11 268 840 53.2
12 259 840 53.2
13 250 845 53.8
14 241 847 54.1
15 233 846 54.0
16 226 841 53.3
17 218 839 53.1
18 210 827 51.6
19 200 819 50.6
20 193 810 49.5
21 185 796 47.8
22 177 782 46.1
23 170 769 44.6
24 163 752 42.6
25 154 736 40.8

1.5 Rev CW
no. Bar FPS FPE
1 353 759 43.4
2 343 753 42.8
3 335 758 43.3
4 328 756 43.1
5 322 751 42.5
6 315 753 42.8
7 309 753 42.8
8 303 752 42.6
9 296 757 43.2
10 290 760 43.6
11 282 756 43.1
12 274 759 43.4
13 268 768 44.5
14 262 770 44.7
15 255 773 45.1
16 249 774 45.2
17 243 781 46.0
18 237 782 46.1
19 234 786 46.6
20 225 787 46.7
21 218 798 48.0
22 213 797 47.9
23 207 804 48.7
24 198 803 48.6
25 193 793 47.4
26 188 789 46.9
27 180 779 45.8
28 175 771 44.8
29 168 763 43.9
30 162 749 42.3
31 155 735 40.7
32 145 720 39.1

1.75 Rev CW
no. Bar FPS FPE
1 343 705 37.5
2 335 693 36.2
3 328 690 35.9
4 323 698 36.7
5 319 697 36.6
6 313 695 36.4
7 306 691 36.0
8 301 691 36.0
9 295 694 36.3
10 290 690 35.9
11 285 693 36.2
12 280 689 35.8
13 274 698 36.7
14 269 700 36.9
15 264 701 37.1
16 260 702 37.2
17 254 699 36.8
18 247 707 37.7
19 242 708 37.8
20 237 712 38.2
21 232 714 38.4
22 228 716 38.7
23 223 720 39.1
24 218 722 39.3
25 212 725 39.6
26 208 728 40.0
27 202 736 40.8
28 197 737 41.0
29 193 747 42.1
30 187 748 42.2
31 181 749 42.3
32 177 749 42.3
33 172 742 41.5
34 168 746 42.0
35 162 738 41.1
36 156 731 40.3
37 152 721 39.2
38 146 715 38.5

 

[JDGriz]

This is some data for the JSB .25 lead-free pellets, 16.54 gr. I did the tests for the last 3 settings with a lot of dry-firing to get to the lower pressure steps without having to shoot a ton of pellets. I'm not sure what's going on at "2.5 Rev. CW", or how well this would reproduce.

0.0 Rev CW
no. Bar FPS FPE
1 340 1223 54.9
2 328 1182 51.3
3 315 1145 48.2
4 308 1169 50.2
5 296 1138 47.6
6 289 1130 46.9
7 278 1122 46.2
8 268 1104 44.8
9 257 1093 43.9
10 248 1079 42.8
11 239 1066 41.7
12 230 1055 40.9
13 220 1049 40.4
14 212 1031 39.0
15 204 1021 38.3
16 195 1007 37.3
17 187 991 36.1
18 178 977 35.1
19 169 959 33.8
20 159 938 32.3

1.5 Rev CW
no. Bar FPS FPE
1 355 969 34.5
2 346 958 33.7
3 340 960 33.9
4 335 958 33.7
5 330 966 34.3
6 324 966 34.3
7 318 965 34.2
8 313 966 34.3
9 307 971 34.6
10 301 973 34.8
11 296 971 34.6
12 290 981 35.4
13 284 976 35.0
14 278 975 34.9
15 272 975 34.9
16 267 977 35.1
17 262 971 34.6
18 255 978 35.1
19 250 981 35.4
20 245 976 35.0
21 239 979 35.2
22 235 990 36.0
23 229 984 35.6
24 224 988 35.9
25 218 990 36.0
26 213 987 35.8
27 209 991 36.1
28 203 983 35.5
29 198 983 35.5
30 193 980 35.3
31 188 978 35.1
32 184 972 34.7
33 179 967 34.4
34 174 959 33.8
35 168 952 33.3
36 163 944 32.7
37 159 932 31.9
38 154 926 31.5

1.75 Rev CW
no. Bar FPS FPE
1 343 913 30.6
2 337 904 30.0
3 330 905 30.1
4 324 908 30.3
5 318 906 30.2
6 313 903 30.0
7 309 906 30.2
8 304 900 29.8
9 300 897 29.6
10 294 894 29.4
11 289 896 29.5
12 284 891 29.2
13 280 894 29.4
14 275 893 29.3
15 270 893 29.3
16 265 890 29.1
17 260 893 29.3
18 256 890 29.1
19 252 891 29.2
20 248 892 29.2
21 244 896 29.5
22 239 893 29.3
23 235 886 28.8
24 231 896 29.5
25 227 891 29.2
26 223 889 29.0
27 219 890 29.1
28 215 890 29.1
29 211 888 29.0
30 207 883 28.6
31 203 883 28.6
32 199 888 29.0
33 195 885 28.8
34 192 884 28.7
35 188 895 29.4
36 185 887 28.9
37 182 894 29.4
38 178 890 29.1
39 175 893 29.3
40 171 896 29.5
41 168 891 29.2
42 164 889 29.0
43 160 891 29.2
44 156 888 29.0

2.0 Rev CW
no. Bar FPS FPE
1 350 859 27.1
2 345 843 26.1
3 340 846 26.3
4 336 842 26.0
5 332 851 26.6
----------------------------
6 300 838 25.8
7 294 835 25.6
8 289 828 25.2
9 287 834 25.6
10 283 825 25.0
----------------------------
11 250 816 24.5
12 246 815 24.4
13 241 814 24.3
14 237 813 24.3
15 233 813 24.3
----------------------------
16 200 791 23.0
17 197 796 23.3
18 194 796 23.3
19 191 790 22.9
20 189 791 23.0
----------------------------
21 153 788 22.8
22 150 789 22.9
23 147 793 23.1
24 144 793 23.1
25 141 806 23.9

2.25 Rev CW
no. Bar FPS FPE
1 347 792 23.0
2 342 781 22.4
3 338 780 22.4
4 333 783 22.5
5 329 787 22.8
----------------------------
6 301 775 22.1
7 297 778 22.2
8 293 783 22.5
9 289 773 22.0
10 286 776 22.1
----------------------------
11 250 756 21.0
12 247 758 21.1
13 244 754 20.9
14 241 757 21.1
15 239 756 21.0
----------------------------
16 200 736 19.9
17 198 730 19.6
18 196 730 19.6
19 194 728 19.5
20 192 726 19.4
----------------------------
21 154 700 18.0
22 152 702 18.1
23 150 702 18.1
24 149 704 18.2
25 146 700 18.0

2.5 Rev CW
no. Bar FPS FPE
1 345 759 21.2
2 341 753 20.8
3 337 758 21.1
4 333 756 21.0
5 330 751 20.7
-----------------------------
6 300 753 20.8
7 296 753 20.8
8 291 752 20.8
9 288 757 21.1
10 285 760 21.2
----------------------------
11 250 756 21.0
12 247 759 21.2
13 245 768 21.7
14 242 770 21.8
15 240 773 22.0
----------------------------
16 200 774 22.0
17 198 781 22.4
18 195 782 22.5
19 193 786 22.7
20 191 787 22.8
----------------------------
21 153 798 23.4
22 151 797 23.3
23 150 804 23.7
24 148 803 23.7
25 146 793 23.1

 

[Nomadic Pirate 66]

Wow,...cooking at full power !!!

the 1.75 is just wonderful filling to 320 BAR

 

[weevil]

Breaking the sound barrier and getting 40+shots with an ES of 20 at 30fpe. What more could anyone ask from a PCP!

Kudo to you for that hard work, JD!

 

[JDGriz]

Wow,...cooking at full power !!!

the 1.75 is just wonderful filling to 320 BAR

Yes, 1.25 and 1.75 seem (almost) universally good.

 

[JDGriz]

Breaking the sound barrier and getting 40+shots with an ES of 20 at 30fpe. What more could anyone ask from a PCP!

Kudo to you for that hard work, JD!

Cheaper lead-frees

 

[Nomadic Pirate 66]

Question :

when you say JSB.25 you mean GTO ?

 

[weevil]

Question :

when you say JSB.25 you mean GTO ?

Yes - they are not branded as GTO in Europe and are known as JSB lead-free.