• In order to send private messages to other members, you must have a minimum of 10 posts on the site.

Tuning FX Crown MK2 700mm barrel .25 cal 70.8 FPE!


I was tuning my .25 cal Crown MK2 today for the JSB 34g MK2 heavies and I wanted to share the power I was able to get with the new setup. I adjusted the hammer spring pretension to 1/2 turn from max, before hitting the power wheel cam, reg pressure was at 153 bar and power wheel on 5. 
This was giving me every consistent speeds at 967 FPS. I was able to sight it in at 50 yards and I was getting under 1/2” groups! The energy for that speed and pellet weight is 70.8 FPE. I have been trying to see if anyone has posted the top end power that the new crown could put out and i didn’t find any solid answers. Here is a video showing the speed using my labradar. I will add some pictures of groups later when I can shoot at 50 yards and 100 yards. 

Nice rig you got there. Thanks for sharing your numbers. I’ve been curious as to what kind of power the MK11’s were making.

For reference my .25 gen 1 Continuum maxed out at similar reg pressure 153-155.

34gr 905 fps for 61.85 fpe

34gr 960 fps for 69.59 fpe

After modding probe and transfer port.

The new Crown comes with a “huma style” Transfer port already installed on it. I have the actual huma transfer port on several other barrels and even though the Crown has one that looks like the huma, the ports are actually a bit shorter. Here is a picture with the actual Huma dual hole on the right and the one that comes with the Crown on the left. Both are .25 cal ports 


I will be swapping the Huma on to the 700mm Crown barrel and will be boring out the probe to match. In my experience performing these modifications yield better accuracy at high power. I feel like it smoothed out the airflow and that leads to a smoother shot cycle. 

Thanks for sharing your gen1 numbers! Not much of a difference once you modified yours! 
Hmmmmmmmm? these things R gett'n like caring a BAR in WWII when walking in the woods hunting! IMO. JUS maybe the FX Impact/Compact can shed some LBS?

This is a bench gun for sure! I have several areas to shoot prarie dogs and I do so out of the bed of my truck in the prone position. I have a DreamTac Compact that weights 5.5 lbs un-scoped and an Ataman BP17 that is 5.1 un-scoped for walking around! 
Humm, wonder if the difference in the orientation has an effect? Similare in theory, the shoulder angle on a center-fire. Orientation in Huma reg is straight forward while FX is rotated 45° instead of directing the gas forward rather than focusing the gas to the sides of the barrel.

I would think that it would be needed to raise the reg pressure to accommodate the new volume of gas avaible. Makes sense to me.

Thanks, the the settings. I look for to giving them a go. Funny the only difference between my present tune and yours, is reg pressure and weight of my projectile. 600mm Barrel .25 Crown mk2. 

Good topic.