93 Shot String from .22 Vulcan
From Full 250 BAR to about 118 BAR
QUESTIONS:
1) Where did it drop off Regulation ❓
2) Does the Regulator setting change if the HST is changed ❓
3) Is there a Sweet Spot RANGE within the overall Regulated Range ❓
So here is the DATA in FPS:
901, 913, 909, 909, 908, 907, 912, 909, 905, 907,
905, 906, 908, 909, 910, 909, 905, 905, 908, 909, 907, 906, 907, 909, 909, 912, 907, 907, 910, 908, 909, 910, 909,
(195 BAR @ 33 Shots)
905, 906, 912, 907, 910, 909, 913, 909, 910, 914, 907,
(180 BAR @ 44 Shots)
906, 909, 910, 906, 911, 910, 907, 910, 911, 911, 908,
(165 BAR @ 55 Shots)
905, 915, 910, 913, 911, 913, 909, 909, 914, 912, 909,
(150 BAR @ 66 Shots)
907, 913, 907, 910, 910, 907, 913, 912, 918, 914, 916,
(140 BAR @ 77 Shots)
908, 919, 916, 917, 921, 916, 914, 914, 913, 913, 909,
(125 BAR @ 88 Shots)
910, 904, 902, 895, 895.
(118 BAR @ 93 Shots)
Note; the AT Gauge is not perfectly linear so I fudged a couple a little to give the best estimation.
All Replies
if I divide your lowest fps by the highest, it is still less than 4% difference between them, to be honest it is still a “flat line” performance wise.
what you have to do is to shoot groups to find out when groups open up.
I know this because consisten fps does not mean it will also group.
apropos, 30fps up and down in only a few mm difference in POI based on gravity drop.
I would not touch that gun, and if, I would lower even more the fps so you get even more shots. but that would mean lowering both reg and hst.
if you want to get rid of the little rise towards the end it will cost you shotcount. and that is a bit of hts clockwise.
so practically you will not achieve much, it will be flatter i.e. better extremem spread but for less shots. it will be more constant but it will steeply fall off sooner. so whats the point?
This was a good read
http://www.varminter.com/forums/topic/17266-tuning-a-regulated-pcp/
I think you can go up a bit to stretch out the flat portion of the velocity curve to more shots,
but that doesn’t necessarily also mean SD will improve or worsen.
I think you’ll have to empirically adjust up and measure.
The most we can get out of this string is that your regulator seems set higher than expected
and matching the gun knee would be at a higher HST tension than current. I would bet
that a touch higher will let yo get out to 80 shots while staying flat on velocity curve.
Guykuo,
Thanks for the graph and comment ❗
I have the HST adjusted for 18 gr JSBs averaging 910 fps. I thought that would be on the high side for accuracy and was getting sub 1/2″ groups at 50 yards. I don’t know if I should turn it up or not 😐
I also did a running SD at the points where I read the pressure and deternined at this FPS I would have a sweet range of 44 shots from 220 BAR to about 150 BAR.
But now I wonder if I could get even better accuracy at a higher FPS.
Based on where the velocity graph starts climbing off regulator, I’d say it was about 145 bar around shot 71
And since, it rises after going off regulator, your HST is probably tuned “below the knee” (a lower air volume than the regulator will deliver.)
That’ s consistent with the large shot count before going off regulator
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Guykuo,
Thanks for the link. I’ll have to re-read it a mumber of times to digest all the implications.
Kris,
I think I’m beginning to understand the reg function better. Most consistent groups is the most important thing and I hope that is when the SD is lowest. But…
Guykuo confirmed my suspicion that the reg is a little higher than others. For now I will leave it alone and see what other gains I can get out of it. I have a small hord of 18 grainers that will be my standard ammo but I have an assortment of other .22 pellets to experiment with after I settle on the best 18 gr tune.
Donnyfl and some others use 220 BAR for their fill pressure and I wondered if that would be better than my 250 BAR fills. In this 93 shot string the SD was flattest from about 220 BAR to 150 BAR shots #23-66, for 44 shots at 910 fps. That may be different if the my reg was lower like others.
My best 50 yard groups were at 904 fps so I’ll have to check it now at 910. If the groups are better then I’ll turn it up. If worse, I’ll try tuning down.
My .22 Vulcan was a great shooter out of the box and getting better and better.