GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: JungleShooter on September 08, 2019, 07:32:37 PM
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How to Tune the Skyhawk .22 from 32FPE to 38FPE?
I have a Skyhawk .22 with a LW choked barrel, and Huma reg (setting unknown).
It shoots the JSB Domed at 925fps (30FPE) and the Baracudas at 830fps (32FPE, 2FPE more than the JSB).
I’d like it to shoot the JSBs with 970fps (33FPE) and the Baracudas with 860fps (35FPE).
How do I go about this? I’m no gunsmith, but I think between the videos on the tube I’ll figure out how to take things apart and put’em back together without having left-over pieces at the end....
Another question....: Is it even advisable to do so?!?
To understand my situation: :-\
I’ve been trying to evade them, really! – but in the end they still got to me. And now I belong to them, they own me.
Them, that is – the long-range pixies.
I have to blame them for this unrelenting urge to shoot long-range (100y and hopefully beyond), and as they make their high-speed low-altitude passes up and down the valleys of my desert hills, it is their fault that the winds are always howling, soooooo....
I need high-BC projectiles. Which either means (a) heavy domed pellets – (b) or slugs.
By getting the muzzle energy a little higher I’m thinking I would be giving those slugs better stability downrange (the barrel is a LW with 17.7 twist rate, not particularly fast, if I interpret the ...).
(A side benefit of higher muzzle energy: I’ve been looking at all those nice hollow-points with a relatively high BC – H&N Hunter and Hunter Extreme, JSB Metalmag, even the Hades (with a fairly low 0.024BC). These would really open up nicely if they hit my critters at higher speeds....)
Thanks for your help. I got lots to learn here. :)
Matthias
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i'm watching this because i have an offer out to a person wanting to sell
there skyhawk.
according to the owner, its a 33fpe gun with 18.13gr jsb.
i would like to increase that as much as i can and still have stability.
thanks ;)
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If you want to shoot far and kill things, accuracy comes before speed. You are already close to the limits at 925fps. My Taipan and Priest ll will both go into the mid 900’s. They do acceptable out to 50yrds. To get my best 100yrd groups, I have them set around 900fps. The 50yrd groups then improved also. Your Skyhawk is light and made in China, staying around 900 will keep the shot cycle smooth and the gun reliable.
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I am watching also. I want more than the 28 FPE it came with new and to shoot heavier pellets, 25 to 32 grain.
I just got my 22 caliber Skyhawk back from Lee545 having his 25 cal plenum extension put in , regulator set to 140 bar from 130 (Huma). I have the longer 20 inch LW poly choked barrel, so not suited for slugs, and all the required porting.
I have not chronied it yet.
Not interested in slug shooting with it as I already have a 615 yard video on utube on line of me breaking 12 oz cola cans at 500-550 and 615 yards, not to mention I can’t see that far anymore.
More interested in which spring and what preload.
Roachcreek
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Diabolo shape pellets at nearly 1000 FPS?
Nope. I'd focus on heavier pellets, not lighter existing pellets edging on trans-sonic.
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Gentlemen ,
In my experience playing with a variety of guns from the QB78 and through to FX and just about everything in between . Making power is usually pretty straight forward . Big ports , big spring and heavy hammer usually get the job done . Getting the balance right so that the gun is still shootable and reliable . Over stressing components is not something to be taken lightly , overfilling being the worst kind .
Before tearing into these guns , and drilling everything out ,and installing a massive hammer spring . I would go through them carefully and making sure that all the ports are lined up and the air flow is as unrestricted as possible . Having port diameter changes is a real power killer in PcP’s . I’d go to no more than .170” , lean on the hammer spring if needed by shimming before replacing .
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I have the longer 20 inch LW poly choked barrel
Roachcreek
where did you get the LW barrel from and was it a direct fit, or
did you have it machined ?
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Based on you already having a LW Barrel, I would increase hammer spring tension, reduce valve stem diameter to 2 mm and add a power plenum, I have one from Lee AP on this forum and have been working with Huub at Huma Air who sent me a 12 and 16cc power plenum to test, unfortunately both my p15's are being re-barreled to LW and CZ barrels at present, so I have been delayed in testing, HUUB has in the meantime however already brought the plenums to market....
https://www.huma-air.com/Artemis-P15-Power-Tune-Regulator-XL-Plenum-Set (https://www.huma-air.com/Artemis-P15-Power-Tune-Regulator-XL-Plenum-Set)
There some other areas you could gain as well such as porting...Others have already done so successfully...
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My offer was accepted for the used skyhawk.
It should be here this weekend.
A CZ or LW barrel is needed ;)
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Gendoc,
I had JSAR machine the barrel, during the process they asked me what length I wanted as I had asked them to do.
I requested a 20 inch barrel. I got it back just as they were starting the Raptor project.
The LW barrels are undersized and require brass bushings to fit the rail supports I have no idea what the Cz barrel diameters are
My quest for power involves using jsb’s In the 25 to 32 grain range not light weight pellets. When I bought it PA did the 10 for 10 test for me but used 11 grain pellets, go figure. I shot some 14.3 crosman hp’s chronied at 11 yards at 905, so at the muzzle they were going much faster, very accurate but not at all what I wanted so I had the plenum put in and did a order for the heavier jsb’s. I personally have no desire for the lighter pellets at Uber velocity.
I have just put it back together after Lee returned it with the plenum extension, I have mounted a Bushnell AR4.5x18 on it but not tested it yet.
I
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Gendoc,
I had JSAR machine the barrel, during the process they asked me what length I wanted as I had asked them to do.
I requested a 20 inch barrel. I got it back just as they were starting the Raptor project.
The LW barrels are undersized and require brass bushings to fit the rail supports I have no idea what the Cz barrel diameters are
My quest for power involves using jsb’s In the 25 to 32 grain range not light weight pellets. When I bought it PA did the 10 for 10 test for me but used 11 grain pellets, go figure. I shot some 14.3 crosman hp’s chronied at 11 yards at 905, so at the muzzle they were going much faster, very accurate but not at all what I wanted so I had the plenum put in and did a order for the heavier jsb’s. I personally have no desire for the lighter pellets at Uber velocity.
I have just put it back together after Lee returned it with the plenum extension, I have mounted a Bushnell AR4.5x18 on it but not tested it yet.
I
thats good to know, and i hope your performance is to your liking.
now i must find out about the cz barrels and where to purchase a blank.
my taipan has a cz barrel and its very accurate and reliable like we all know the taipans are..... 8)
thank you !!
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I shot the Skyhawk today, went from 2 turns in on the spring, then worked up to 4.5 turns then back to 4 turns in on the hammer spring.
Still very quiet but then I have a longer, larger diameter shroud to mate with the 20 inch barrel.
Right now in duct seal, 22cal 25.39 Jsb’s are very quiet and accurate, maybe shot 15 8 shot one hole groups.
My cheap chrony has passed on, the battery terminal will not take the 9 volt ends and touching the terminals does not breath life into it. Being as indoor chroning and light is a problem, I am considering the wireless fx chronograph as the fact it works in the dark is a heads up for indoor chronygraphing.
So to test my Power without a chrony, I measured penetration into duct seal. My 500 fps prod buries 14 .3 grain pellets flush to the skirts, my Seneca 25 carbine puts 43 ej’s Into duct seal to where they are 1.25 inches to the skirt, the Skyhawk duplicates this penetration.
My regulator is set at 140 bar, without the extended plenum, at 130 bar, I was getting around 905 at 33 feet with 14.3 hp’s and 70 shots, 820 FPS with 18 grains. The Skyhawk is now getting around 40 shots.
So what does the penetration comparison mean?
It may mean that it will shoot 25.39 grains flat for 400 yards and then start rising! Most likely though it means my chrony is broke, sort of like having a broke speedometer and rear ending cars to test your speed.
Regards
Roachcreek
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I shot 4 darko mags with the 14.3 Benji’s, they shoot little one hole groups like before, still very quiet, but those 40 shots took the tube pressure to 120 bar not 140 bar, so 3500 psi to140 bar is around 32 shots.
So it would seem I must be taking benefits from the plenum extension, noise being low leads me to think the shroud is working fine and not pushing that double dose of air out the muzzle.
I feel confident that I am making a lot more polite power, meaning subtle sound and great accuracy, but I am going to need to spend a couple hundred bucks for a pcp speedo to know for sure.
Regards,
Roachcreek
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I ordered a Caldwell chronograph and light kit to replace the non working, never working inside chrony.
A pcp owner should never be without a speedometer.
I am really liking the way my Skyhawk turned out.
Roachcreek
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Thank you all for chiming in. 😊
I'm still eager to hear more comments on how to tune up the power.*
And on the wisdom (or folly) of doing so in the first place.
*(not to 40 or 50FPE, but say 36 or 38 max.)
Roachcreek,
it sounds like you have a real nice gun now. I have accompanied your Skyhawk journey from terrible shooter to terrific shooter — and I'm happy for you that it worked out!
Matthias
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Okay I have some Skyhawk numbers.
Lee545 plenum extension
20 inch LW poly chocked barrel
Huma set at 140 bar
Brand new Caldwell chronograph 3 feet from muzzle and 12 yards from muzzle
JSB 25.39
Two turns in from flush=859 FPS at 3 feet, 828 FPS at 12 yards.
3 turns in = 874 FPS /43 FPE
Next I will try the 32 grain JSB.
First I need to stop giggling.
Roachcreek
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Okay I have some Skyhawk numbers.
Lee545 plenum extension
20 inch LW poly chocked barrel
Huma set at 140 bar
Brand new Caldwell chronograph 3 feet from muzzle and 12 yards from muzzle
JSB 25.39
Two turns in from flush=859 FPS at 3 feet, 828 FPS at 12 yards.
3 turns in = 874 FPS /43 FPE
Next I will try the 32 grain JSB.
First I need to stop giggling.
Roachcreek
wow!!!
tell us more about Lee's extension 8)
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Well 33.9 5 were doing 755 FPS which again is 43 FPE.
Yes the Lee 545 25 caliber plenum. If I remember correctly, Lee 545 made it for the 25 caliber P-15, but it obviously works on the 22. It screws onto the valve body and the end of the Huma, fitting in between the regulator and the valve, doubling the plenum volume.
I had trouble getting it sealed as I ran out of divers grease and I just don’t have enough vision left to sort it out. Lee was making me a replacement shroud to correctt the bum workmanship of SnowPeaks p15 shroud, so I just asked him to install it which he easily did.
He charges 77 bucks for the extension.
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I appreciate the info, thanks! ;)
Makes me wonder if I need this plenum extension, too....
Need, yupp, in airgunning those things aren't wants, but needs...!! ::)
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Yes John and Matthias you need that plenum extension!
I did some more work with my chronograph, but this time I set things up better, for the Chronograph angle to meet the Skyhawks angle, and I shot at 10 yards.
My highest velocity with the 25.39 22 JSB was 857 FPS, which corrected to the muzzle is 904 FPS/46 FPE.
Basically I picked up 18 FPE with the plenum extension and more preload, but bear in mind I have a 20 inch barrel.
I also have to say how much I am enjoying the Bushnell AR Optics 4.5x18 as I can see the reticle so clearly.
Roachcreek
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i will be checking in with Lee, thank you !!!!
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My highest velocity with the 25.39 22 JSB was 857 FPS, which corrected to the muzzle is 904 FPS/46 FPE.
Roachcreek,
you bring up something that I have been wondering about:
🔸Where to place the chrono —
🔸and what muzzle velocity number to use in my balllistic calculator....
You write you "corrected to the muzzle".
🔸Is that necessary?
🔸How do you do that?
Thanks for enlightening my ballistic twilight. 🤣
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Gendoc,
I had JSAR machine the barrel, during the process they asked me what length I wanted as I had asked them to do.
I requested a 20 inch barrel. I got it back just as they were starting the Raptor project.
The LW barrels are undersized and require brass bushings to fit the rail supports I have no idea what the Cz barrel diameters are
My quest for power involves using jsb’s In the 25 to 32 grain range not light weight pellets. When I bought it PA did the 10 for 10 test for me but used 11 grain pellets, go figure. I shot some 14.3 crosman hp’s chronied at 11 yards at 905, so at the muzzle they were going much faster, very accurate but not at all what I wanted so I had the plenum put in and did a order for the heavier jsb’s. I personally have no desire for the lighter pellets at Uber velocity.
I have just put it back together after Lee returned it with the plenum extension, I have mounted a Bushnell AR4.5x18 on it but not tested it yet.
I
thats good to know, and i hope your performance is to your liking.
now i must find out about the cz barrels and where to purchase a blank.
my taipan has a cz barrel and its very accurate and reliable like we all know the taipans are..... 8)
thank you !!
Pyramid Air - replacement barrel for the CZ 200 :)
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Matthias,
I placed the chronograph directly in front of my target, I shot from 10 yards. Using the AA AIRGUN CLASSIFIED bullet calculator I increased the velocity until it matched my 10 yard velocity I achieved on my chronograph, then read my 1 yard velocity on the ballistic calculator.
I hope this makes sense.
Roachcreek
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Roachcreek, that makes sense, thanks.
My Skyhawk seems to spew something out besides just 15.89 grain pieces of lead....
Wonder if this is normal (it's my first PCP, still got to learn lots).
Anyhow, it seems like there is something like water vapor (🤔) coming out, for about a foot or a foot and a half beyond the muzzle I can see it....
Any clues...? 🤔
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Pyramid Air - replacement barrel for the CZ 200 :)
i have been instructed that these barrels are too short for the skyhawk.
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Okay I am getting very close to 47 FPE and do get a few at that power at the height of my regulat4d string.
So let’s talk about shot count:
Before the plenum extension I was getting around 70 28 FPE shots with 14.3 Crosman HP’s.
After the plenum extension, and with a hammer spring adjuster flush with the receiver, I was at 40 shots@42 FPE with 22 cal 25.3 and 33.9 grains.
Now at three turns in I am at 46.67 to 47 FPE I get 36 shots before dropping off the regulator.
Bear in mind I am not filling to 3625 psi, I am filling to 3500 to 35504 PSI. This is due to the fact that the P-15 design blows out the fill port oring if I creep over 3625 PSI and I get tired of replacing that oring for the sake of a couple more shots I don’t need for the trouble it is to get them.
Roachcreek
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who makes the regulators thats in the skyhawks ?
mine is a gen-I.
reason i ask is, the huma power plenum is what i'm interested in.
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Matthias,
Sorry I missed your question about the water va-er coming out of you Skyhawk. It sounds like your inadvertently putting water in your rifle. How do you have your high pressure air?
John,
I think Snowpeak makes their own regulators. You can buy them on eBay, but I never read the adds.
Roachcreek
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Handpumping w/ FX 4-stage.
65ºF / 18ºC
85% humidity
30" Hg / 1015mB
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Matthias,
Pressurized air can lead to condensation also, having said that 85% humidity will give you moisture in your airgun. Some hand pumps, such as the Hill mk4 and I think the mk3 have moisture filters.
I live in the High Desert, I have around 35 to 45% humidity in my air conditioned house and I run a air filter on my Shoebox inside the house. When I was pesting on the vineyards in western Oregon the humidity was very high and My scba ranks would spit air when I filled some think this can cause corrosion in PCP tanks, I always inspected my airgun tanks for corrosion and have never noticed problems. The writer of the Pyramydair blog, Tom Gaylord says it just shoots out the moisture when you shoot the your airgun.
So the jury is undecided, I however run moisture filters and check my air gun tubes when I depressurize and work on my airguns.
Hope this helps.
Roachcreek
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Regarding seeing a small vapor cloud when shot. I use dive shop scuba air and I will see the vapor trail on occasion. In my case and since very dry air is being used I'm thinking it is more related to moisture in the air and if the temp of the gun when shooting is warmer than outside temp.
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Pyramid Air - replacement barrel for the CZ 200 :)
i have been instructed that these barrels are too short for the skyhawk.
Who told you that ? These barrels are over an inch longer than OEM - Lee just did mine -See below:
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I also reduced it by a few mm to have the same thread as original p15/ skyhawk
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Pyramid Air - replacement barrel for the CZ 200 :)
i have been instructed that these barrels are too short for the skyhawk.
Who told you that ? These barrels are over an inch longer than OEM - Lee just did mine -See below:
maybe i was mis-informed, it happens from time to time on the web....
was it Lee 545 that did your barrel machining ?
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Pyramid Air - replacement barrel for the CZ 200 :)
i have been instructed that these barrels are too short for the skyhawk.
Who told you that ? These barrels are over an inch longer than OEM - Lee just did mine -See below:
maybe i was mis-informed, it happens from time to time on the web....
was it Lee 545 that did your barrel machining ?
Yes it was he had no problem doing it...comes threaded 1/2 unf but I wanted it changed as i wanted the stock shroud...
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Pyramid Air - replacement barrel for the CZ 200 :)
i have been instructed that these barrels are too short for the skyhawk.
Who told you that ? These barrels are over an inch longer than OEM - Lee just did mine -See below:
maybe i was mis-informed, it happens from time to time on the web....
was it Lee 545 that did your barrel machining ?
Yes it was he had no problem doing it...comes threaded 1/2 unf but I wanted it changed as i wanted the stock shroud...
i understand about the stock threading, i have a Rocker1 custom LDC coming
in that thread.
do you have the Huma power plenum installed in yours ?
and BTW....thatsa very nice look'n skyhawk you got there !!!
i bet she is a sweet shooter...8)
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Pyramid Air - replacement barrel for the CZ 200 :)
i have been instructed that these barrels are too short for the skyhawk.
Who told you that ? These barrels are over an inch longer than OEM - Lee just did mine -See below:
maybe i was mis-informed, it happens from time to time on the web....
was it Lee 545 that did your barrel machining ?
Yes it was he had no problem doing it...comes threaded 1/2 unf but I wanted it changed as i wanted the stock shroud...
i understand about the stock threading, i have a Rocker1 custom LDC coming
in that thread.
do you have the Huma power plenum installed in yours ?
and BTW....thatsa very nice look'n skyhawk you got there !!!
i bet she is a sweet shooter...8)
Yes she is custom built from scratch P15 in 177 Caliber, custom stock and many internal mods, modified spring, hammer, valve stem , larger Transfer Port and many others, just finished assembling her last week, she is a 177 caliber and yes it has HUUBS Power Plenum and Reg from Huma. I spent some time encouraging Huub to develop one, he sent me and one other lucky guy plenums to test... 12cc plenum - lower reg pressure shooting JSB 10.34 at 915 fps, Reduced hammer spring tension and I am getting somewhere around 70 -80 shots per fill...Lost count last time around :) Lee is your guy to do the barrel, shot 50 pellets at 28 yards through a thumbnail size hole and she has not been leaded in properly...Extremely accurate...
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from the huma power plenum page, it asks for this information...
IMPORTANT NOTE BEFORE ORDERING:
Artemis/Spa/Diana uses different ways of machining inside the pressure tube. To make sure we will sent you the correct model we need to know the position of the "step" inside the pressure tube as shown on the picture below. Size X can be smaller as 82 mm or larger as 82 mm.
Please select the correct model of your pressure tube in the drop down menu in the order field.
anyone here ordered the power plenum for the skyhawk and know what this
inside "step" Dimension is ??
i thought that the only difference was cosmetics and branding ??
but i am wrong occasionally..... ;D
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I tried shooting 14.3 Crosman Ptemier hp’s this morning with the preload backed out to flush.
I wanted to see what amount of adjustment I could get with the plenum installed and if the velocity was stable at low hammer spring preload. I had sketchy chronograph readings before the plenum was installed, but if memory serves me correctly, it was in the 900-910 range after tuned by JSAR.
I fired a magazine of the 14.3 Crosman at 10 yards from the Caldwell chronograph and then calculated the velocity to the muzzle using a bc 0f .025.
The result was I had a range of muzzle velocity from 910 to 915 psi, most shots were 910 to 915 FPS.
So it appears I can have a FPE range from 23 FPE to 47 FPE simply by adjusting the stock hammer spring. I find this amazing for a regulated rifle.
Riachcreek
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Roachcreek, that is amazing!
Very cool. Now I'm wondering if I need to get that plenum extension after all.
I read on the Huma website that there are two types, and I basically would have to take the gun apart to know which one fits mine.... 😟
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Matthias,
Having just had plenum extension installed in mine, I wish I knew which one you need so that you do not need to tear your Skyhawk down to determine which variation you have.
I just purchased the one Lee545 makes. However, with my lack of useable vision and Divers grease, I could not “seal the deal”.Needing more work done, along with Lee45 offering to seal it up for free, it was an offer I could not refuse.
Sure worked out, I love this Skyhawk now, but would have most likely loved the Taipan Veteran I could have purchased for what I paid for this rifle.
My advice is: contact Lee545 here on this forum or Airgunnation, buy a Huma regulator from Huna, buy the plenum from Lee545, tear down your rifle, ship only the air tube down to the valve along with the new Huma regulator to Lee545 and have him seal it up and return it. Your only shipping a air tube so if Peru has regulations about shipping and receiving guns of any kind I would not think you would have a problem, if theY do not have such restrictions, take the stock off and send the entire action to Lee545. You would be better off shipping the entire action to Lee545 to ensure it is totally sealed.
Lee545’s work he did on my rifle was superb, and I have had rifles made by the best.
Roachcreek
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Thank you for your sound advice, Roachcreek! 👍🏼
Good thinking about the shipping to Peru! 😄 Yeah, shipping is a bit complicated as stuff gets lost in the mail all the time.
I usually just have a friend bring stuff down when they visit.
My situation is that I already have the Skyhawk with the Huma installed.
🔸Maybe I just should start playing with the HST and see what I end up with....
HST — that's the big screw on the back of the receiver, right? (Sorry, I'm really new at this.)
Any recommendations on how to go about this HST tuning stuff? (I'm prepared to drill a half moon into the stock so that the HST is fully exposed for easy adjusting without taking off the stock every time....) 😊
Matthias
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Matthias,
Did you install your regulator?
You can sand in a half moon cut to access the hammer spring adjustment, however unless you have a large enough volume of regulated air you won’t see much results.
JSAR Installed my Huma, Matt increased the regulator to almost maximum, at the same time he increased the hammer spring tension but the meager results were not worth the effort of running everything at max, the volume of regulated air was just not there, so I had him set the regulator to 130 bar.
This setting yielded what I now get with the plenum extension with no hammer spring preload and 140 bar set on the regulator.
With the plenum extension and my regulator at 140 bar and setting the HST at 3.5 turns I enter the low 4o fPE range and still have more HST to work with.
That extra volume of air is what makes the difference.
The regulator screws into the valve assembly, the extension is threaded on both ends to screw onto both the Huma regulator and valve assembly and sealed up by the orings, if you installed the Huma yourself, you could most likely install the plenum.
Roachcreek
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Roachcreek,
I did not install the reg...
And hearing you talk about your Skyhawk with 40FPE makes me want to just get the extended plenum...! ::)
WHY are so many of us so hungry for POWER?!?!?! ::)
If I mess up the installation (got zero experience), I'd be "grounded" from shooting for a long time (shipping the parts the US, getting it fixed, finding someone to bring them back).
But if it works, it probably will do wonders for my dream of slinging slugs, not just pellets.
Of course, 40FPE would severely limit my choices of which pellets I still could shoot at that power:
I made a chart that shows me the options of pellets that a given muzzle energy permits me. I attach it below.
So, no more JSB 16 nor 18g.
No more Polymag, Hades, etc.
No more Sniper Magnums, Baracuda Hunters, and all that. 😟
I'd be left with only these — hoping that at least one will shoot great groups: 😟
In Pellets: Baracuda, Piledriver, Monster and Beast (that's only 4!)
In Slugs: 5 NSA slugs, and a couple of the other smaller slug brands.
Not sure if I should risk it (and $80). I'm thinking...!! ???
🔶 Anyhow, Roachcreek, how many shots do you get now on a full tube?
Matthias
Attachment:
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Matthias,
I shoot both 14.3’s and 25.39 in my Skyhawk, both Weights can be shot at close to the same velocity. However with the heavier pellet I need to increase the hammer spring tension so that the valve opens further and more air is released behind the pellet.
3.5 turns in on the HST and I am in the 40 plus FPE level. I turn the HST out to where it is flush or no turns in, meaning less hammer spring preload, and shoot 14.3 grains at 24 FPE or so.
How long the valve stem stays open is referred to as dwell time, other things such as projectile weigh, barrel length, travel time in the barrel, can influence dwell time but We will keep it simple with what we are doing so let’s simply look at hammer spring preload, which is really just how hard we want to hit that valve stem with the hammer.
Just because my plenum now has more air because I extended it, does not mean I have to use all of it each shot.
Basically I have a extended plenum full of 140 bar air, how much of the air I use each shot from the plenum depends on how hard the valve stem gets hit, the harder the hammer strikes, the valve is open longer and the faster the projectile travels, and thus uses more air. I turn down the hammer spring preload, and the valve is open for a shorter duration, dwell time, and less air is used and the projectile goes slower.
I have not counted them but I seem to get a lot of shots with the 14.3z@ 910 FPS , around 40 shots @43 fpe with 25.39’s, and around 35 at 47 fpe.
So you should be able to use 14 grains through 25.39 and heavier if you wish with the extended plenum but you will have to adjust the HST for different weights depending on how fast or slow you wish them to go.
Installing that plenum yourself will mean you should have a lot of orings for your rifle, a good supply of divers grease and better eyesight that me.
Hope this helps,
Roachcreek
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Matthias,
Shoot that rifle the way it is and see if it serves your needs. Learn how it works, watch the 5 disassembly video series on P-15 disassembly.
Your the best judge on what you want and the ability to make it happen, considering where you live, ability to get parts through your mail service and being comfortable with your abilities.
This regulator/plenum mod on the p15/Skyhawk is picking up interest and there will be more threads on the pro’s and cons and practicality of the mod.
Roachcreek
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Roachcreek,
thank you so much for all your good advice and explanations! 👍🏼
(1) I think I will up the power a bit to get the JSB 15.89 going at 970fps = 33FPE, just dialing the HST. That way I have a little more power for the next step — slugs:
(2) Then I will test shoot all the slugs I can get my hands on and see if I can find one slug that groups well at 100y.
If I do, I will try to be content and leave good enough alone.
(3) If I do not find a suitable slug, I will try to up the power to by dialing a few more changes (regulator setting, I think):
18 grainers at 970fps = 38FPE
Another round of slug testing.
(4) If I still can find a slug that groups well, then I will try the plenum extension and take the dive to up the power once more:
for the 21g Baracuda at 970fps = 44FPE.
You talk about changing the power settings in order to adapt the power to the weight of the pellet. Well, that in theory is a nice idea, but once I have my gun, scope, and ballistic calculator set up, I really don't want to mess it all up with a few turns on the HST screw.... (a non-repeatable change...).
Thanks again! Guns are so much fun!! 😄
Matthias