Tuning Crown MKII velocity question

[Corvid_hunter]

I have a new Crown MKII .25cal with a 600mm barrel. Factory tune has the reg set about 110-115 bar. Shooting the JSB 25gr Kings I'm getting about 830-835fps with the transfer port on High and the HS wheel on 24 (max). When I switch the transfer port to Medium the velocity increases to approx 840-850fps. I haven't pulled out the barrel to see if it's set on the pellet or slug transfer port side, but I don't think this would make an issue like this. Why is the velocity increasing when I set the transfer port to Medium?

 

[Jlowe]

Because your reg is set low for a .25cal. You HS may be low, but the reg needs to be up to at least 130 bar. My 500mm .25cal Crown MKII will do over 970fps with 25 grain JSB's, but the reg is at 150 bar. You should be able to get away with a lower bar setting, but not that low. 

 

[pesty3782]

I have the same barrel on my crown….my reg is at 145 transfer port on high and I think I am at 21 on hammer spring…shooting the 34 grain at 930. I did tune the hammer spring on 24 so there was very little play…It took awhile to get this tune, but it shoots great.

‘Tony P

 

[gfmiller58]

I have a similar set-up: 0.25 caliber Crown Mk II with 600mm barrel (using the dual ports). With regulator set at 140 bar, transfer port on high and the hammer spring maxed out it was shooting 25.4 grain JSB's at 998 fps. Lowering the regulator to 130 bars increased muzzle velocity to 1015 fps. To achieve higher velocities I think I'd need a heavier hammer and/or hammer spring to work at higher regulator pressures.

George

 

[Corvid_hunter]

Thanks for the replys gentlemen. I think I will increase my reg in 5 bar (or so) increments until the Max transfer port and #24 on the power wheel are around 925fps with the 25gr JSBs.