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FX Crown Tuning Contradiction Questions

Forums PCP Airguns PCP Airgun – Discussion FX Crown Tuning Contradiction Questions

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    WolfCobra
    Participant
    Member
    Accuracy: +0

    Happy Saturday, everyone! I recently purchased an FX Crown (my first PCP), and decided I wanted to try out the JSB MKII heavies to see if I could get better long range results (100+ yards) with the higher BC over the standard 25 grain JSBs. It came tuned out of the box with a regulator pressure of ~122 psi (per the rifle's pressure gauge), and I started working that pressure upwards in an attempt to get the MKIIs closer to the mid-800 fps range, from ~780 fps stock. below are my chrono numbers for 5-10 shot strings, as measured by a Magnetospeed V3 on high sensitivity. 

    130 psi – Avg: 811    S-D 20

    135 psi – Avg: 817    S-D 5.6

    140 psi – Avg: 788    S-D  1.0

    Without touching the hammer spring adjustment wheel (it remained on MAX for all testing), it is clear that my rifle liked the higher regulator pressure from a consistency standpoint. My only question is this: why would I see a decrease in velocity by increasing from 135 psi to 140 psi? This drop was repeatable over several attempts at testing the different regulator pressures. Do I need to take the rifle out of its stock and increase the hammer spring tension? I have not yet found a good tutorial showing that process, including which direction to turn which screw, and how far… Ted from Ted's Holdover mentioned he went until he felt an increased tension on the screw, but is that the method preferred by most? It was much more accurate at 50 yards at the higher regulator pressure, but I would much prefer a higher muzzle velocity to help out with the top end of the rifle's range.

    Thank you very much for your advice, I'm very happy with my rifle so far, and I would love to be able to tweak the most out of its performance while also making sure that I know what I'm doing. 

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    Tweeter
    Participant
    Member
    United States
    Accuracy: +18

    The more you increase the reg pressure the harder the valve is to open, simple as that.  You need to add more hammer spring tension as you raise the reg pressure to see an increase in velocity?

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    Tweeter
    Participant
    Member
    United States
    Accuracy: +18

    I can't help with the tuning process as I dont own a crown but here is a great vid (if you haven't seen it already) that may help.  Good luck!

     

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    JoeKool
    Participant
    Member
    United States
    Accuracy: +37

     

     

     

    With all do respect, the regulator pressure reading is bar not psi, had to correct you…  Anyways, yes your  regulator’s pressure setting is probably fighting against the strength of your hammer springs tension setting. (It can’t buck the high force exerted by the 140 bar pressure) I also have a .25 FX Crown.  Adjusting your hammer spring internal tension screw adjuster is best done over a chronograph.  To truly max it out you don’t just screw it in until it stops.  If you do that your Crown will be out of harmony as Ted put it.  I speak from experience.   ✔️What you must do is adjust the HST screw a half turn at a time (clockwise) and take about 3 to 4 shots over your chronograph and note the velocity.  Repeat this until you reach you desired fps.  If you notice that the pellet speed / velocity / fps starts to discontinue to increase or actually decreases, back off (counterclockwise) until your velocity reaches its highest fps.  Leave it there, thats your true max setting.  Its tedious and annoying but thats what it takes to max out your  FX Crown.  Put your gun back in the stock and then just use the external HST knob to tune for pellet speed.  You may find that “4” works for JSB 25.39’s. and “5” is good for JSB 33.95’s.  140 bar is my Crown’s regulator tune and it is perfect for me!

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    Michael
    Keymaster
    Keymaster
    Accuracy: +155

    Tweeter

    The more you increase the reg pressure the harder the valve is to open, simple as that.  You need to add more hammer spring tension as you raise the reg pressure to see an increase in velocity?

    Agreed, here's a picture of my impact, the crown is similar except you have to remove the stock. Insert an allen key shown in green and extend (turn in) the Allen screw to reduce the amount of play in the black floating rectangle. This will increase your hammer spring. Be sure not to adjust your regulator above 150 bar as it will likely cause it to seize up or damage it. Keep in mind those little manometers are not very accurate so I wouldn't get too close to the 150 mark.

     

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    Crusher
    Participant
    Member
    United States
    Accuracy: +29

    Here is an Ernest video showing how to do it on an impact. But it works exactly the same on the Crown. You don't want to take up ALL the slack at once. Mine had significant play in the little piece that slides in this video. I took about about 80% of that slack and brought my Crown up to 925 fps. with 25's. I have tuned it a bit since then. Having the reg up to 140+ without increasing the hammer spring is the reason your velocity dropped.

     

    Hope this helps

    Crusher

     

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    WolfCobra
    Participant
    Member
    Accuracy: +0

    Thanks so much to everyone for the explanations! I feel like a knucklehead for the psi vs bar mixup, but hey, bar never landed on the moon… :D

    The two keys are understanding that the reg pressure is working against the hammer spring and the knowledge that it is going to be a pain to go ahead and test each half turn of the screw until the velocity stops increasing. That at least gives me the confidence to push forward and do so, realizing there isn’t an easier way. 

    Is there any danger to shooting the Crown without reinstalling the stock? That would make tuning a lot easier, and I can do do safely into a backstop, while still getting chrono data. 

     

    Thanks all!

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    2D1C
    Participant
    Member
    United States
    Accuracy: +24

    No I took my stock off re-installed the power wheel and tuned away!. I suggest re-installing the safety as well!!

     

    Dennis

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    JoeKool
    Participant
    Member
    United States
    Accuracy: +37

     

    Is there any danger to shooting the Crown without reinstalling the stock? That would make tuning a lot easier, and I can do do safely into a backstop, while still getting chrono data. 

     

    Thats what I did!  With-out the stock tuning.  “BUT”, remember you have no safety because you remove it to pull the stock.  Unless you reinstall it without the stock.  Be careful, it is very easy to accidentally bump the trigger without a trigger guard or stock.  Also, kind of awkward.  Be safe and good luck!

     

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    samirkilachand
    Participant
    Member
    Accuracy: +0

    Hi,

    I just got a Crown .30 with 600mm barrel. The Reg was set at 147 bar and I increased the hammer spring tension to 15mm. I’ve put two tins of JSB 44.75g

    however, my FPS Is really low. Here’s my last shot string as measured by the FX wireless chrony 

     

    Shot count: 6
    Low: 759
    Hi: 835
    Avg: 788
    Spread: 76
    STD Dev: 25.5
    835
    784
    775
    759
    784
    789

    i don’t understand what I’m doing wrong. I zeroed the rifle at 30m and it is pretty accurate. However I would like to get the FPS upto 850-870 so that I can shoot out to 100-120m.

    Could anybody give me some advice please?

     

    sam

     

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    2D1C
    Participant
    Member
    United States
    Accuracy: +24

    Did you note the hammer spring measurement before you adjusted it? if so take it back to that setting and shoot it a couple hundred times and let the gun settle in then see what you have.

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    swissarmyknife
    Participant
    Member
    Accuracy: +0

    One extra piece of advice while fine tuning the HST is to give the regulator time to recharge to the expected pressure. If you have a setup that allows to shoot pellet upon pellet than you might get some inconsistencies from not allowing the regulator to recharge fully.

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    swissarmyknife
    Participant
    Member
    Accuracy: +0

    samirkilachand

    Hi,

    I just got a Crown .30 with 600mm barrel. The Reg was set at 147 bar and I increased the hammer spring tension to 15mm. I’ve put two tins of JSB 44.75g

    however, my FPS Is really low. Here’s my last shot string as measured by the FX wireless chrony 

     

    Shot count: 6
    Low: 759
    Hi: 835
    Avg: 788
    Spread: 76
    STD Dev: 25.5
    835
    784
    775
    759
    784
    789

    i don’t understand what I’m doing wrong. I zeroed the rifle at 30m and it is pretty accurate. However I would like to get the FPS upto 850-870 so that I can shoot out to 100-120m.

    Could anybody give me some advice please?

     

    sam

     

    Back to basics: Start off with the hammer spring tension at the highest setting, meaning that you can just rotate the power knob lobe past the setscrew. Then take a few shots over the chrony and turn the setscrew CCW maybe 2 x 1/4 turn and repeat the chrony measurement. Repeat this as you take average chrony speeds after each adjustment and also graph the average. You will eventually see a peak and then it will reduce speed again. Right after that peak is usually where the ES and SD come with the lowest spread.

    I shot hundreds of pellets of different shapes and weights through my Crown during these fine tuning tests and also noticed that the pellet itself has a big impact on consistency. That could be due to manufacturing tolerances, design, deformation of the pellet or all of the above. Ultimately I use the heaviest pellet the crown liked and fine tuned that using max power and then adjusted the transfer port and power setting for different types of pellets creating a cheat sheet that tells me what setting to use for various different types. This paired with a ballistic compensation allows me to switch between pellet types and be nearly on the same POI with minor scope adjustments.

    Also I am not sure with .30 if the 147Bar reg pressure is sufficient to shoot 44gr pellets the speed you want. Conceivably should be OK as I manage to shoot 30gr .22 at around 860 with lesser surface area, so should be possible.

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    Bob_O
    Participant
    Member
    United States
    Accuracy: +106

    There IS a quicker and easier way, I did it with my Crown and will work with the Impact as well.

    1. Set the D5 adjustment screw so you have maximum compression of the HS with the hammer wheel on MAX.  Make sure the screw does not protrude into the circular recess that the cam rides in.

    2. Use the hammer wheel to make adjustments during tuning, starting at position #1 and work your way up.  The markings go like this: MIN, E, 1, D, 2, C, 3, B, 4, A, 5, MAX.

    3. Use the adjustment screw for fine tuning only, after  you've made the gross adjustment with the wheel.  

    4. Set the adjustment screw to the length that corresponds to the MAX setting once you're done tuning, if desired.  

     

    • This reply was modified 1 year ago by Bob_O.
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    samirkilachand
    Participant
    Member
    Accuracy: +0

    Thanks! I’ll try this. Quite excited to get back to my yard and start plinking away ;)

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    Long_Gun_Dallas
    Participant
    Member
    United States
    Accuracy: +21

    Tweeter

    The more you increase the reg pressure the harder the valve is to open, simple as that.  You need to add more hammer spring tension as you raise the reg pressure to see an increase in velocity?

    This.  I've found the crown hammer to be ineffective for operating pressures above 135 BAR.  Though, you can raise your pressure to stabilize your consistency.  As it will put you a bit over the gun's power curve peak (on the other side, lower than)

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    Bob_O
    Participant
    Member
    United States
    Accuracy: +106

    Though it could be inconsistencies between gauges, I found very little gain going above 150 bar.  

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    samirkilachand
    Participant
    Member
    Accuracy: +0

    Thanks. The crown came from the factory at 147 bar but the hammer spring tension was too low for that and was getting low 700’s FPS. 
     

    ive increased the hammer spring tension now getting High 700’s but I suspect that the reg pressure may be too high. I’m gonna try backing it down to 140 bar and seeing what happens and slowly putting it up.

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    Bob_O
    Participant
    Member
    United States
    Accuracy: +106

    The AMP reg can handle 160bar no problem.   

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    samirkilachand
    Participant
    Member
    Accuracy: +0

    My manual says it goes to 160 bar but then below it says not to increase it past 150 bar so not sure ?

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