Help on Jkhan Nobleese .25 FAC Bullpup

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redsea

Member
Jan 16, 2019
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Rhodos, Greece
Hello everyone!!!

This is my first post hire as i need you help on my new Jkhan Noblesse .25 f.a.c bull pup.

I order it from Spain after i have spend much time reading on forums and watching you tube video reviews for this airgun.

The gun came 20 days ago and i was very happy.

Yesterday i took it out for a crony test and i got disappointment from the numbers i was getting compare with other Jkhan Noblesse owners.

Hire are the result of my crony test using jsb 25.39 grains pellets.







Any idea what it can be wrong?
 
I had a .25 Noblesse rifle, and suspect your 200 BAR charge pressure is too low to find your bell-curve power-band for the power setting your gun is currently at. Two options- increase your charge pressure, or reduce your power (back off the hammer-spring power adjuster).

Here's what I got with my .25 Noblesse after testing and adjusting-

34 grain King, power adjusted, 3250 PSI fill, 20 shot powerband= Low- 833, Hi- 857, ES- 24, SD- 4, Average-843 FPS/53.6 foot-pounds


 
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HI AirNGasman and thank you for your answer!!!

Isn't 200 bar the max. fill pressure for the Jkhan Noblesse bullpup?

I tryed today your advice and back off the hammer-spring power adjuster and crony 5 shots for each adjustment using 25.40 grains jsb pellets. Hire are the results:

1.) FLAT SPOT ( The back of the hammer spring tension flat with the back of the receiver of the gun)

200 bar





  1. - 1 turn from the flat spot
    [/LIST=1]

    200 bar





    3.) - 2 turns from the flat spot



    200 bar





    4.) - 3 turns from the flat spot

    200 bar



    Something is wrong I guess???



    Most of them starting from +-1.000 ft filling from 200 bar with 25.4 grains JSB and they even suggest to cut the OEM spring 1-2 coils to slow it down, when I start from 910 ft. at 200 bar.



    Check this American you tube video review for the Jkhan noblesse Bullpup from 5:43 to 6:35

    https://www.youtube.com/watch?v=l_cr9tb76AM

 
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Red, from your post it seems you're increasing the hammer-spring tension (and power), rather than decreasing. If so, you're going the wrong direction. 

I watched that part of the video, and would suggest you not cut 2 coils off the hammer-spring. That caused their sweet-spot fill pressure to drop WAY down. Assuming you'd like to maintain high power but get more, and more consistent, shots per fill without charging over 200 BAR you should shorten the hammer-spring as little as needed to locate a fill pressure that returns a good power band of usable shots.

I'd recommend cutting 1/2 coil off the spring at a time, and chronographing each time with 200 BAR fills until you see a reduction in velocities. The ideal power band is achieved when velocities start about 20-30 FPS below where it peaks (5-10 shots later). Velocities should linger around peak velocity for another 5-10 shots, then steadily decline for another 5-10 shots before falling below the starting velocity (20-30 FPS below peak velocity).

EXAMPLE- 200 BAR fill (or thereabout), velocity starts at 875 FPS and climbs steadily over the next 10 shots to 900, lingers around 900 for 5 shots, then for the next 8 shots steadily falls to starting velocity of 875 FPS for a BELL-CURVE POWERBAND of 23 shots from 875 to 900 FPS.

I hope this helps.


 
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Thank you AirNGasman!!!! I was decreasing the hammer-spring tension turning the bolt counter clockwise( no clockwise). That's why i thought that something must be wrong.

I do not understand why other jkhan Noblesse owners with the O.EM. spring , filling 200 bar and having the back of the O.E.M hammer spring tension flat with the back of the receiver of the gun as i do , can archive 1.000 ft/sec and more and i only get 900 ft/sec....????

There must be an explanation for that that i would like to find out first before i go feather.

If you can Help me with that, or anyone else to solve this problem out it will be great, and then i will go easy easy to the next steps for tuning this air gun.

I am asking you again if you know: What is the maximum pressure that this air gun can be filled?
 
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Thank you oneshot61 for your reply!!!

I am using the gauge of my fill tank and not the rifle gauge.. I am filling the gun at 2900 psi also ( 200 bar) . I know that my shots are not fast as it supposed to be compare with others owners and i am trying to find out why. do you have any suggestion on possible things to check on the air gun that may cause this problem? 
 
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Howdy! I would suggest checking alignment of the transfer ports between the various parts that the air passes through. I don't have experience with your rifle but as I open up mine pcp I see alignment problems . And I can imagine this could be pretty common.

If the alignment is off, then air flow would be limited. In my gun I found poor alignment between the valve and the main block. There was also discrepancies in the sizes of the ports.

All of this takes away power. Fwiw, my gun benefited from less hammer steike and a slightly higher fill pressure.
 
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"What is the maximum pressure that this air gun can be filled?" I think 200 Bar/2900 PSI is the factory recommended fill pressure, and it would be irresponsible of me to suggest exceeding that on a public forum. Assuming PCPs are proof-tested WAY ABOVE recommended fill pressures, I (personally) don't hesitate to go 10% above recommended pressure. 

A couple times I have seen reducing hammer-spring pre-load (tension) actually increase velocity, but won't speculate exactly why. 

When you say others with the same gun as your's achieve 1000 FPS, is that also with 25.39 grain pellets? I'd be surprised; but could see 14-16 grainers going that fast. 

Mcoulter makes some good points about transfer-port(s) alignment. That might be a good thing to check.

Regardless, your gun is wanky for some reason, and the idea is to search for the source of the inefficiency(s). Other possibilities that come to (my) mind are a canted, kinked, or broken hammer or valve spring, or a bent valve-stem. 

Please keep us posted, Red.
 
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Did you buy the gun brand new,or was previously owned ?

I had a brand new (around 2 1/2 years ago) , and the very first shot coming out of that gun ,was at 980 fps .

Then ,I've decided to change the original hammer spring ,for a softer one from McCarr,and ,was getting the chrony numbers in the mid 800 ,with great results .

So,if you bought the gun "used" ,maybe, it doesn't have the OEM hammer spring .
 
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Hi oneshot61 and thank you for the reply to my post!!!

I agree 100% with you that something goes wrong with my air gun. I had all ready on my mind to check transfer ports between the various parts for alignment like you suggested me!! So through the weekend I will strip the gun to check every part for issues.

Hi AirNGasman and thank you for the reply to my post again!!!!

I will stay for now….:) with the 2900 psi fill pressure until I will find out the problem.

When i said others owners with the same gun as mine achieve 1000 FPS, yes ,they where using also 25.39 grain pellets just I did.

I will post their crony numbers. I will check all the things that you have mention!!!!!



Hi Rami939 and thank you for the reply to my post!!!

I bough the air gun brand new 20 days ago fro Spain.

Hire is the link of the shop

https://armasayala.com/gb/air-compressed-rifles-pcp/821-jkhan-noblesse-bullpup-air-compressed-rifle-walnut-stock.html

The gun came with 2 magazines and 2 hammer spring ( One short for low velocities and one Long F.A.C ) . I took out the short out and replace it with the O.E.M f.a.c hammer spring.

I have send e mails to the shop that I bought the gun about my problem and they reply that they do not understand my massage at all……… and they only shelling the airguns….

They suggest me to speak with the manufacture ( jkhan) as I did by send him an e-mail but until now I haven’t had any reply back fro him.

So I decide to ask your help through this forum.

Do you guys now if the O.E.M hammer spring is the same for both calibers ( .22 and .25)?

Can someone tell me please the damnation's of O.E.M hammer spring to compare it with mine?

Thank you all!!!!! and sorry for my bad English.....
 
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Hi Rami939 and thank you for the reply!!!!

I measured my O.E.M spring and the dimensions are not the same compare with after market one that you gave me. Hire what I have:

L: 78 mm ( 3.07’’)

OD: 11.6 mm ( 0.46’’ )



Wire : 1.4 mm ( 0.055’’)



Today I strip the gun down and searched for issues. I could not find any so I reassembly it making sure that there is an alignment on transfer ports between the various parts and test it tomorrow. When I was there I measured the transfer ports of the barrel and the transfer port of the block and both of the where 4 mm ( 0.157’’) .The trancfer fort of the valve was 4.5 mm ( 0.177’’) .



Aren’t the transfer ports small for .25 caliber air gun?



Does anyone know the transfer ports size of this gun in 0.25 caliber so I can compare if I have the same size?



Another thing I noticed is that it was hard to push in with my finger the valve stem of the gun even the air tube was empty because of the hard spring in the valve .



Is that normal with this gun?
 
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