Tuning Tuning my FX Crown mk2 .30/.25

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danny5692

danny5692

Member
Nov 17, 2020
75
81
friesland, Netherlands
Hey There.

I have bought me a .30 FX Crown MK2 a few months ago.

Right out of the box it was shooting pretty sweet with some 1 to 2 inch groups at a 100 yards with the 44 grain jsb's MK2. So far so good for a beginner like me.

I have also bought me a .25 barrel kit and have started to tune the rifle with the 33 grain jsb's. I have used the method from Meathead Marksman, turning the hammerspring to max and with every shot on turn back(1/6th rotation). That worked fine and I found a sweet spot at about 16 turns back.

Now the .30 was set out of the box to 24 turns back from max hammerspring tension. I have tuned the riffle again with the .30 and came to the conclusion that this is the correct sweet spot.

My question is: how is it possible that a smaller caliber needs more hammerspring tension than a bigger caliber? One should think the opposite is true?

Now I am shooting my .25 at max on the hammerwheel, and my .30 at nr5 on the hammerwheel.

.25.1626856110.jpg
.30.1626856110.jpg

 
Any time when you lower HS a setting in the wheel and not have much speed drop then you are wasting air and potentially affecting accuracy. To get to the sweet spot you need to lower the HS stick you get that fist significant drop around 20-30fps and that’s your sweet spot. If that sweet spot is too low then increase regulator and repeat the exercise till you find the sweet spot again. Once found the sweet spot then turn down the valve and scrub another 20FPS then you have yourself a well tuned impact. 


example: your target speed is 900 FPS, while valve is at wide open or around 4 lines.

HS 3: 890

HS 4: 920

HS 5: 940

Max: 950

HS 4 is your sweet spot and then turn down the valve till you get to 900fps. That method will get you the most consistent, efficient and accurate tune on an impact.


Every gun is slightly different so how many turn on the preload screw is mostly useless because it would be different on every gun. The different between sweet spot and not is very small but pretty easy to find on the impact. Write down your setting for each caliber which in turn will get you very close next time you switch ammo/caliber.
 
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Doh!! Just ignore the valve part but everything g else applies. 


mad far as finding sweet spot the it’s speed difference between different hammer wheel settings. If all setting has 20-30 FPS difference the. You either need to increase reg or increase preload. You can only find the sweet spot if you see a plateau in speed increase when increasing Hammer wheel setting. 
 
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I think there is an misunderstanding.

When I use the hammerwheel atm I can see fps drops from 20fps to 30fps. That works fine.

But when I tune the gun, the fps drops per 1/6th turn on the fine tune of the hammerspring are not 20 to 30 fps drops. Those drop max 10 fps per 1/6th turn of the screw. 

According to my diagram I picked 16 1/6th turns from max on the fine tune(from maxed out hammerspring). That looked like the beginning of a plateau? My groups look ok and the deviation is about 2 to 3 fps. 

I suppose this setting is fine, the question was more; how could a .25 caliber ask for more hammerspring power compared to .30 ?
 
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So when tuning just use the HS wheel. Since all your HS settings on your wheel have a speed delta of 20-30 FPS then either lower your reg or increase the preload or small Allen wrench by 5 full turns till you find the plateau. Don’t use the Allen wrench for finding the sweet spot, it’s for move the HA range ups and down or very find tuning/move your sweet spot/a specific HS wheel setting up/down 5fps. 
 
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