I need proper direction on how to tune an unregulated PCP rifle, any help is greatly appreciated.
The correct way to tune an unregulated PCP rifle
- Thread starter perazzisc3
- Start date
Tune it how? Nice bell curve? Open it up for more power? What gun? Got to have more to go on than that.
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I found this and it is a bit more detailed than what I used to do so better.
https://docs.google.com/file/d/0B8TulutA1DY9U1phdWpBNWluckk/edit?pli=1
https://docs.google.com/file/d/0B8TulutA1DY9U1phdWpBNWluckk/edit?pli=1
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Hatsan Nova Star, do I adjust the hammer spring after fill up of 250 bar or at a lower bar. I am trying to get 925 fps for a 18.13gr jsb.
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A few more questions for you...
1) Do you have a chronograph? If so, how is it shooting now?
2) Assuming you have a chronograph, have you shot a full string and graphed the results?
Not knowing these answers, I will make a couple of general statements based on a couple of Hatsan PCPs I own (a Flash and AT44 each in .177).
I got the flash new and found that it was shooting hot but quickly loosing velocity with each shot. Graphing the shot string it looked like a "cliff". It had too much change in velocity for my tastes. In simple terms this was corrected by reducing the tension on the hammer spring and filling to a slightly lower fill pressure. This resulted in the "bell curve" RJ mentioned above. Instead of consistently loosing velocity from shot #1, the gun gained velocity, then held steady, and eventually the velocity dropped off again.
Here's a graph showing the Flash's original performance:
And here is a later tune. Sorry the chart styles are visually different, but you should get the idea.
A big part of making this happen is to find the best balance between fill pressure, hammer spring tension, and pellet weight. You should plan on testing the velocities your gun produces at different hammer spring settings. Here again is my flash testing. As you can see there is certain point where adding more and more hammer spring tension fails to produce more velocity. (Oh, this is also with different pellets than the chart above...) In fact you'll probably hear you gun getting louder and wasting air at some point.
Hopefully this points you in the right direction! And I'm sure folks a whole lot smarter than me will add plenty more to this discussion!
1) Do you have a chronograph? If so, how is it shooting now?
2) Assuming you have a chronograph, have you shot a full string and graphed the results?
Not knowing these answers, I will make a couple of general statements based on a couple of Hatsan PCPs I own (a Flash and AT44 each in .177).
I got the flash new and found that it was shooting hot but quickly loosing velocity with each shot. Graphing the shot string it looked like a "cliff". It had too much change in velocity for my tastes. In simple terms this was corrected by reducing the tension on the hammer spring and filling to a slightly lower fill pressure. This resulted in the "bell curve" RJ mentioned above. Instead of consistently loosing velocity from shot #1, the gun gained velocity, then held steady, and eventually the velocity dropped off again.
Here's a graph showing the Flash's original performance:
And here is a later tune. Sorry the chart styles are visually different, but you should get the idea.
A big part of making this happen is to find the best balance between fill pressure, hammer spring tension, and pellet weight. You should plan on testing the velocities your gun produces at different hammer spring settings. Here again is my flash testing. As you can see there is certain point where adding more and more hammer spring tension fails to produce more velocity. (Oh, this is also with different pellets than the chart above...) In fact you'll probably hear you gun getting louder and wasting air at some point.
Hopefully this points you in the right direction! And I'm sure folks a whole lot smarter than me will add plenty more to this discussion!
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I have a NovaStar.22. You mite find it hard to get it to shoot around 925fps with the 18s. Slowest mine will hit with those 18s is 976fps average over 70 shots. You could that the spacer out of the hammer spring or clip a coil.
You may want to try the redesigned monsters 25.39, mine really likes them at about 900fps.
Butch
You may want to try the redesigned monsters 25.39, mine really likes them at about 900fps.
Butch
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Thanks this is helpful. I do have a chrono. My Nova Star factory settings was shooting the 18.13gr a little too fast I think. I lowered the hammer spring power and found that low to mid 920's fps they flew true. The trouble I am having is after refilling the carbon fiber bottle to about (240 bar) the fps dropped to 860 fps and I shot til 150 bar and the fps never went back to above 900. I reset the power and checked the chrono and had attained 930 fps and then refilled the CF bottle and the power was 830 fps. I am trying to understand and with a little more info I might get it . Should I set the power at a certain bottle fill level? I know that with a full 250 bar the power would be lower to start and as the fill level goes down the fps should go up but I think when I adjust the hammer spring I may be doing so at the wrong CF bottle fill level.
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Yes, you need to fill to same psi/bar, shoot the same pellet, one that you know is accurate in your gun, and tune with your hammer spring adjuster. If your results are not what you want, you have a large velocity spread between shots, then try doing the same tuning at a lower fill pressure. Do this until you get a fairly even fps spread of like 20-40fps max, depending on the range you are shooting at, difference between shots. I would say that you likely need to tune at a slightly lower pressure than your last round because you don't want a 100fps change in velocity in your string. If you want shot consistency and a decent shot count you can't be overly picky on the velocity you end up with. Although you can always change to a lighter pellet and tune again to increase your final velocity spread.
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It's a PDF file most systems read them fine. Try it with a different computer or go online and get the reader it's free.
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Got a new Nova Star .22. But first testings showed that the gun only makes around 16 ft/lbs with 16gr pellets out of the box. Thats a big disappointment. and the barrel shroud is interefering with barrel alignment. When the shroud is on the pellets fly everywhere. Without it is very accurate but weak as you see. I will send it back. This is unexceptable. But does anybody know what the problem with the power can be?
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There can be multiple problems with the gun doing that. Breech seal, barrel seals, bottle seals to name name a few. I have done ALOT of work done to mine and it is very accurate but as I said ALOT of work. There is one major flaw with this rifle and It is the way they attach the bottle/valve to the gun. If I was you I would send the gun back for a refund. Just saying this from what I know with me gun.
Butch
Butch
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I was aware of some problems that could have come up but having this crap right from the start really makes me doubt in the overall quality and reliability of the gun. I´m gonna send it back and save up for something better. Thank you Butch for the reply.
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Shot string with JSB 18.13, from 200-110 bar
828, 39, 40, 41, 37, 41, 44, 49, 41, 46
843, 43, 47, 50, 49, 51, 53, 53, 50, 54
850, 53, 54, 53, 54, 52, 54, 51, 52, 54
853, 56, 54, 53, 50, 57, 52, 58, 56, 56
857, 32, 58, 61, 62, 65, 64, 63, 60, 62
861, 61, 61, 58, 63, 65, 61, 61, 65, 64
864, 62, 63, 63, 60, 60, 62, 62, 62, 61
863, 61, 61, 62, 58, 57, 57, 59, 60, 58
859, 56, 54, 53, 55, 55, 50, 52, 42, 52
851, 49, 48, 48, 36, 48, 39, 48, 32, 43
I changed the hammer spring with longer softer and took of the spacer
Also i opened a little the barrel TP because it wasn aligned with the block TP
From 250-170 bar i get 65 shots at 39 fpe with 25 fps spread
I took of the "shroud" (its not shroud) only a sleeve at the barrel and its more accurate from triple the price guns
828, 39, 40, 41, 37, 41, 44, 49, 41, 46
843, 43, 47, 50, 49, 51, 53, 53, 50, 54
850, 53, 54, 53, 54, 52, 54, 51, 52, 54
853, 56, 54, 53, 50, 57, 52, 58, 56, 56
857, 32, 58, 61, 62, 65, 64, 63, 60, 62
861, 61, 61, 58, 63, 65, 61, 61, 65, 64
864, 62, 63, 63, 60, 60, 62, 62, 62, 61
863, 61, 61, 62, 58, 57, 57, 59, 60, 58
859, 56, 54, 53, 55, 55, 50, 52, 42, 52
851, 49, 48, 48, 36, 48, 39, 48, 32, 43
I changed the hammer spring with longer softer and took of the spacer
Also i opened a little the barrel TP because it wasn aligned with the block TP
From 250-170 bar i get 65 shots at 39 fpe with 25 fps spread
I took of the "shroud" (its not shroud) only a sleeve at the barrel and its more accurate from triple the price guns
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I've talked to the dealer. I didn't know about the legal power limit in Spain. It's 24 Joules. So therefore they must have done some modifications to the gun. Probably a weaker hammer spring. Because I can only crank it up to around 35 Joules. Does anybody have suggestions what else they could have changed? It's hard to get in contact with Hatsan.
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You will most likely need to get the full power hammer spring and the transfer port also. If you need help getting it apart just post and I will help you the best I can. The gun is easy to take apart.
Butch
Butch
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