Kral Arms Tuning Unregulated PCP - Running out of Hammer Spring Adjustment

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CanMike said:
Okay so port size staying put at where it is. I’m surprised how many shots I got. It’s only a 260cc tube. I’m going to try the longer hammer spring. It’s funny some versions of this action are over sprung and some under sprung I guess. Weird.
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Yes, Benjamin/Crosman uses a 3.5” spring in the Krato/Cayde/Akela .177 & .22s. This results in the .177 being massively oversprung and the .22 also being oversprung. (Use 2.5 to 2.57” for .177 and use 2.8” for .22).

Reximex was on the right track (shorter springs) with Daystar .177, as mine came with a 3.1” spring from their factory.

It seems like they went a bit too short with the spring in your .25 Daystar. Easy fix.
 
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EPG said:
Yes, Benjamin/Crosman uses a 3.5” spring in the Krato/Cayde/Akela .177 & .22s. This results in the .177 being massively oversprung and the .22 also being oversprung. (Use 2.5 to 2.57” for .177 and use 2.8” for .22).

Reximex was on the right track (shorter springs) with Daystar .177, as mine came with a 3.1” spring from their factory.

It seems like they went a bit too short with the spring in your .25 Daystar. Easy fix.
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Spring Ordered from Crosman. Should have it in 1-2 weeks..

To change it you just pop the retaining pin and the old spring pops out? Or is it better to unscrew teh adjustment screw all teh way out and get the spring out that way?

Mike
 
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CanMike said:
Spring Ordered from Crosman. Should have it in 1-2 weeks..

To change it you just pop the retaining pin and the old spring pops out? Or is it better to unscrew teh adjustment screw all teh way out and get the spring out that way?

Mike
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Just pop the pin - and keep your thumb on back of adjuster - so it doesn’t come flying out.

The first time I ever took the spring out of my .177 Akela, I didn’t keep thumb on adjuster and it came flying out of rifle and hit my wall, lol.

Its far less “lively” now that I shortened the springs.
 
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You are getting the best of the best when it comes to advice here. When I went to the underworld of PCP last winter all of these fine gentleman were very helpful with all of my dumb questions especially Dr. Kralenstein as he has the same gun I have. I eventually went with a Huma regulator on my Kral Puncher Jumbo. I also did some advanced modifications as I am comfortable with mechanical tom foolery. I opened up my ports to one size less than 3/16" first. Then I took the hammer out and shortened it while also putting in a shorter dual spring arrangement. I also took all the trigger parts out and polished them to a mirror shine and lubed it all. The only trigger part I failed to remove was the part that actually contacts the hammer. I recently removed it as my trigger wasn't very easy to pull with the dual spring setup. I polished that part all up and put everything back together. Unfortunately while re-assembling the trigger parts the very last part you put in snapped on me....................ARGHHHHHHH! This is not good because Kral parts are like going gold panning very hard to get. The parts are made out of some very cheap substance that I would barely call metal. I think they call it "pot metal"? I was going to try and braze it back together but that immediately showed it wasn't going to work. So I cut a piece of thin aluminum the same size as the bottom of the broken part. Then I mixed up some JB Weld and put the part back together with the piece of aluminum holding it all together. I let it sit for 2 days so that I knew it was fully cured. And the gun is back to working again normally. I tuned my regulator to 140BAR and fill the bottle to about 225BAR. With JSB Exact Jumbo Diablo 15.9 gr. I am getting 876 fps avg. ES of 16 SD of 4 fps. I was using the 15.9 pellets because they didn't have the 18.1's but recently I ordered 1,000 JSB Exact Jumbo Heavy 18.13 gr. as the gun seems to like those the best. With those pellets I am seeing 821 fps avg. with an ES of 19 fps and an SD of 5 fps and an average energy of 27.13 ft/lbs. I know I can get a little more out of the 18's because my power adjuster was turned down a little bit for the 15.9's to get the accuracy just right. I did some testing with the Crosman Premier 14.3 gr. pellets and they were screaming fast at 973 fps with an ES of 21 fps and a SD of 7 fps. The average energy with those was 30.11 ft/lbs. Unfortunately the accuracy was just not to be had. I would get 2-5 hits on target then I would get a flyer or two for no apparent reasonand I think it is just too fast for those pellets. I'm going to do some more testing with the 18.1's this week and open the adjuster all the way and see what numbers I get.
 
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I think I figured out my issue.. Just took the existing Hammer Spring out to take a look and mine is only 70mm, while it should be longer.. This explains why I ran out of Hammer adjustment.

From what I gathered the Spring should be 95mm...

I probably got the low power spring installed in the rifle.



Reximex Daystar & Pretensis Hammerspring​

Replacement hammer spring for the Reximex Daystar & Pretensis air rifle.
11.35mm diameter, 95mm length.
 
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It may not be an issue. You may have a better spring. It’s not about the spring length, it’s about wire thickness. If a gun comes with a 95mm spring, the first thing a guy who knows how to tune a gun will do is go with a shorter heavier spring. Hammer bounce in any gun, regulated or not is your worst enemy. If you manage to get a longer spring for your gun, measure the wire thickness compared to yours. If it’s less, toss it. If it’s the same, pay attention to how your gun sounds as get get down to 150b and less. Go with the spring that your gun sounds the cleanest with. Regardless of a couple of FPS. After all, you should be after accuracy first.
 
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Interesting observation

So I have my 70mm spring with the adjuster all the way in adding 12mm or so.

I picked up a couple 92mm springs and dialed the adjusted all the way back. So comparing 92mm and 82mm spring basically.

With the extra 10mm I lost FPS. Dropped to 720 from the 820 I was getting. So I assume over sprung now. I though if over sprung you would plateau.

Unfortunately only had a few minutes to pop these springs in so didn’t have more time.

Weird about the drastic drop.

I should mention the new longer spring may be heavier and I think I’m very close to max on my short spring. (Probably need only a few mm more) So probably 10mm over sprung with longer one.

Mike
 
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CanMike said:
Interesting observation

So I have my 70mm spring with the adjuster all the way in adding 12mm or so.

I picked up a couple 92mm springs and dialed the adjusted all the way back. So comparing 92mm and 82mm spring basically.

With the extra 10mm I lost FPS. Dropped to 720 from the 820 I was getting. So I assume over sprung now. I though if over sprung you would plateau.

Unfortunately only had a few minutes to pop these springs in so didn’t have more time.

Weird about the drastic drop.

I should mention the new longer spring may be heavier and I think I’m very close to max on my short spring. (Probably need only a few mm more) So probably 10mm over sprung with longer one.

Mike
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What is the wire thickness on all the springs?

IMG_6289.jpeg
 
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Mike.
I´ll be happy to help, have had - and still keep, a few Daystar. Work on guns.

The Daystar by any measure HAS to be the easiest pcp out there to soup up today. I´ve had my 25 spit 42´s (mag limits this) at an easy 1060.

Now i keep a regulated (Huma) 22 where i run 218 dia 22 cal JSB regular Knockout slugs extremely accurate at 1050 approx. Use it for rat control at and around the shop mainly.

It is modified however.
First tip is to replace the hammer spring with one for an FX Impact and that installing a small "shim" to make up for difference in length. Of course you can replace that with basically any spring of the same dimensions and K value. The value of the FX spring though is that i KNOW it to be manufactured the same way proper valve springs for a car is. They´re actually made here in town.
A 25 cal running on system pressure (no regulator) in 25cal will hand downright insane performance already on 5.5mm transfers. A 22.. ditto.
Already as is, out of the box, just with the stock power adjuster valve with the 4mm hole and the hammer spring turned all in we´re at 60 Joules for a 25.

Porting is where it´s at though. The issue however is that the power valve runs on a 6mm dia body which limits how far you can take that porting.
Thus my current 22 runs on a 9mm reamed hole for said adjuster and thus works very very well as is - on 5,4mm ports (22cal) and "sane" reg levels (approx 160 bar)

To retain performance what i´m saying is that first up a different hammer spring is needed and then.. porting. It is however so simple to pull off anyone can do it. Flow path is very short and very much ontap, but that being said the boys at Rex sure did something right cause.. these guns flow you won´t believe.

8.jpg


Here my current 22, per above. It´s nothing short of insanely accurate. You´re all this being said given good advice on how to tune a hammer spring vs shot count and so on, no argument on that note from me.

However. I´m the devil on your shoulder telling.. you haven´t even CLOSE to unleashed what the Daystar is capable of. Yet. ;)
 
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So quick update.. I added a 10mm spacer onto the hammer, so this added some weight and allowed me to find the plateau with the stock spring.. Plateauted at around 880/890 so I dialled back and were at about 875 FPS on JSB 25.4s.

Going to get so,e accuracy data shortly at 30yards.. Should be able to get 50yards during the week and maybe I can fiddle with the new springs I ordered but pretty happy with the spacer / added weight hammer idea.

This is also on a 3.6mm transfer port. So technically I have 0.4mm moe if I wanted to drill it out a the power adjuster operates on 4.0mm I believe.

Mike
 
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Quick update. Did some tuning with the help of a friend across the pond and opened up the ports and upgraded the hammer spring to an impact hammer spring.

Moved up to the JTS 29.6 grain pellets.

If you take the zone from 165 - 200 BAR I’m getting 20 shots with an ES of 8

That’s pretty good for an unregulated gun:) almost Panthera like ES.

230BAR - 875 FPS

—-

220 - 885

—

210 - 890

205 - 903

200 - 913

197.5 - 916

195 - 913

190 - 910

190 - 913

190 - 915

185 - 914

185 - 919

180 - 919

175 - 912

175 - 911

170 - 914

170 - 914

165 - 911

160 - 905

155 - 895

150 - 900

150 - 893

145 - 892

140 - 885
 
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