How to Tune the Skyhawk .22 from 32FPE to 38FPE?

[JungleShooter]

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.... 😟

[Lani52]

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

[JungleShooter]

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

[Lani52]

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

[JungleShooter]

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:

[Lani52]

 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

[Lani52]

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

[JungleShooter]

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