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FX Crown hammer presetting for shooting JSB King Heavys and new velocitys

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PCPair

Member
May 17, 2015
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Groningen
I did some testing with the hammerspring presettings and was able to get the JSB kings Heavy up to a speed of max 850-860 fps by following the YouTube video instruction. It really starts at minute 5.



In my case maxing the screw out resulted in the gun shooting higher on the 4 hamersetting than the MAX setting. Pressure about 130 bar. I do not know what causes this but i turned the screw back in so it had more play on max and this resulted in a more balanced hammersetting. MAX giving the highest velocity as you would expect.

Now the gun shoots the JSB King Heavys at 835fps on max at about 132 Bar. MAX=835, 5=810, 4=750. For some reason i get a vertical spread with the MK1 pellets (onsorted by weight) on 96 meters. On 50 meters it stacks the pellets on top of each other. Does anybody know if the MK II are better shooting?

​For the standaard JSB Kings 25,4 grain, I get the following results. MAX=935, 5=910, 4=880.

Regards,
Jan Peter
 
 I think the reason your velocity went down when you maxed out the setscrew is that you're hitting the valve open so hard that it's actually bouncing closed again faster and therefore your velocity decreases. If you wanted to squeeze out a higher velocity after that. I think you would have to increase your regulator pressure so that the valve has more back pressure behind it. 
T
 
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I've done some extensive testing with the Crown to attempt to resolve the issue of high ES and SD with my crown. LDP on another thread labeled "Tuning Discussion" gave some really good insight into the process.
I've taken that information and performed a little experiment that I'll share with you guys.


Important Notes:
1. Using a Digital Reg Gauge connected in place of my regulator gauge to ensure my regulator was set at each setting. (Reg Pressure was taken at 230 Bar Tank fill)
2. The hammer spring measurement denoted in the tables represents the caliper reading in inches from the leading edge of the hammer spring block to the end of the clearance slot for the allen wrench.
3. I shot a "poop LOAD" of pellets doing this testing!!!!

Here are my results (Each value represents a 5-shot "shot string":
ab6b438da4a3b9d6b299fcfb11d9f74b.jpg


Observations:
1. The valve system of the crown seems to be more stable at 140 Bar as noted by the lower ES/SD numbers posted. this for me resulted in less of a vertical spread at 75+ yards.
2. Once the hammer spring gets high on the plateau (read "LDP's post on "Tuning Discussion"), the valve becomes unstable and the ES/SD moves all over the place as noted in the graphs. 

For "My Gun", the best setting was right on the knee with reg set at 140 Bar, Velocity moves between 845-855, My hammer spring measurement on Max is set at 0.6700. 

I'm currently testing at different velocities and so far, 845-855 is best from my first day of testing this weekend.

Now, with all of this testing, I'm still not beating my Boss or Impact "in the wind" but the crown barrel has huge potential with the way it shoots the 25.4s with no wind.

I think we are all trying to get the heavies shooting in the crown as good as it does with the 25.4s. I'm beginning to believe that the barrel sleeve that has shipped with our guns may need a different twist rate in order to maximize the potential of the gun and reach the same level of accuracy "at distance" as the 25.4's.

I may make a video to help illustrate the testing technique as there are many other observations that I found very interesting.
 
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FoxMan. That is some great information and a great way to lay it out visually for us learners. You have done an astounding amount of work. Thank you for sharing. I am reaching the same conclusions. Not quite matching the Boss and Impact yet, but close. I'd really like to get my hands on the other twist rate barrels to experiment with. What I was hoping and striving for is to get the gun to shoot both the 25 and 34 grain at the peak tune for each with just the exterior settings. Thats asking a lot. Throughout all of your testing what has your impression been on the number of flyers? I'm seeing a dramatic reduction. Sylvan
 
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Kitplanenut, 
I've not had a lot of flyers when I clean the barrel, the barrel gets very dirty as you probably have noticed. My issue has been related to shifts in impact point. It will stack 3 pellets in the same hole, then stack two more 1/2" somewhere else, then put one back in the original hole. I thought it was related to the changes in velocity but when shooting through the chrono after tuning, its not directly related to velocity. 
After this weekends testing, I removed the barrel to see how close it was to my impact and determine if I can install it on my impact. I would need a compatible moderator and machine a divet for the barrel retainer screw for the impact. I'm not confident enough yet to modify the barrel as I don't know what is beneath the machined sleeve base that is different on the crown.
In my testing, the optimal regulator pressure is different for the 34s and 25s. While you may be able to find a happy medium that shoots both well, At this point, I haven't found a point where both would perform as well.
You could try 140 Bar setting moving the 25s at 890 and see how it likes it. You should be able to do this setting your hammer spring in the 6700ish area on Max and moving the wheel to around either 3 or B.
 
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FoxMan good info. 

Do you itend to shoot just the heavys or also the standard 25,4 grain pellets. If so at what velocity does the gun shoot at MAX, 5 and 4.

I would like to be able to shoot booth and think at some point there is a trade off. As mentioned in my topic i also get a vertical spread with the heavys on 800 or 830 fps with the heavys MK1. Spread on 96 meters is 6 to 7 cm (2 and a half inch). I noticed that on a higher velocity of 850 this still is the case with your settings. Do you shoot the MK II Heavys?

My 2011 standard 25,4 JSB Kings shoot extremly well at 96 meters (900 fps) Hammersetting at 5. I will post some picture later.
At 50 meters with standard JSB Kings 2016 batch i got bad grouping at hammer setting 5 (900 fps). When the hammersetting was set to MAX, resulting in 925-930 FPS grouping was a lot better. So not every peller is the same. So test at different speeds. Grouping at 96 meters was not as good at 96 meters though with the 2016 JSB 25,4 grain,

Hope to test the JSB 2017 standard Kings tonight.
 
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PCPair, I'm attempting to shoot the heavies for EBR so that's what I'm focusing on. I did confirm that the 25.4s work best in my gun at 125 Bar at 890 fps. They are very accurate at 75 yards without wind. Add Wind, not so much. EBR is like a freaking tornado after lunch so if 34s don't work, then back to the Boss or Impact.

My 25.4s are from AOA in 2016, just ordered another set so we will see how they do if I get time or I just can't get the 34s to outshoot the Boss or Impact.

My MkII's like 850ish. If I slow then down to 830, the groups open up with every other shot being a flyer. 1.5 to 2" group at 75 at 830. 850 at 140 Bar, they tighten up considerably, but still not quite where it needs to be.

I'm with KitplaneNut on this one, I think we need the 1:28 twist rate barrel to experiment with and I those aren't available to normal folks like us yet. Anyone else think Ted might have one? lol

 
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Was told that the first batch of Crowns included a few of the other twist rates, but when I got mine the rate was not mentioned. I was just happy to get what came, so there may be a few of the other twist rate out there. MAY being the oprative word here. One thing I personally have observed is that with the 25 grain's I have never seen such outstanding accuracy. Just amazing. Like FoxMan I'm trying to set up the 34's for the wind at EBR. Even though I haven't achieved quite yet what my Impact and Boss will do it's still damned accurate. Lately I've been playing with the harmonics. I can see changes, but can't say for sure what's real. Wish I could take ME out of the equation. It's probable all a moot point. EBR will be decided by who can read the wind best. In 2015 it blew my half full water bottle off the shooting bench. Sylvan
 
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FoxMan,

​I shot the JSB 2017 Wednesday at 50 meters and 96 meters. The shoot extremly well at 50 meters and showed great potential at 96 meters. Settings 880 fps hammersetting 4 and 132 bar. The JSB 2017 differ from the 2016 and seem to shoot better than the 2016 JSB. At 50 meters a ragged hole.The 2011 JSB shot great as well.

​I added a picture to show that the 2107 JSB is different. This pellet seems to shoot with a higher velocity as well with the same settings. 970 fps at MAX but than they shoot to hot and the group opens up at 50. The 2016 JSB seemed to like 925-930 FPS better than 900 fps. At 900 fps grouping at 50 was terrible. I added a picture to show the difference between the pellets.

​JSB 2017 skirt is not as deep. 2016 and 2015 look the same, 2011 (also shoot extremly well) has a thinner skirt. Polymag and H&N did not shoot bad at 50 meters. Not as good as the JSB 2017 though but for hunting more than sufficient. Is your BOSS a .30. I shoot a FX bocat .30 at the 100 meter benchrest competition in the Netherlands (indoor)

94384072bfbe8ea3c7935e1bea72d22b.jpg



I only shot 5 5 shot groups at 96 meters the best was 1.5 cm center to center (second image) before i ran out time because of the intensive testing on 50 meters. Just finished a dutch review.
scope 20x and shot with mildot holdover The good thing was that pellets started to drop on top off each other. That is always a good sign (onsorted)

68e1f0c0a87969a6605f5527f53f487f.jpg



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581612f2d24c5f28b1f651ee0dc7a6a1.jpg
 
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