I'm in the process of tuning my Crown to attempt to use the JSB 34gs at EBR 2017 this year. So to define my goal, is very predictable pellet placement at 75 and 100 yards. Just as everyone else, my crown came shipped at 125 Bar moving 25.4s at around 890 and 34s around 790. Average ES was about 16-20 fps when I got it. EBR 2017 typically is very windy so I believe if I want my best chance of success shooting in the wind, I need to get the 34s shooting well if the Crown is going to come with me. Otherwise, I'm going to use the Boss. It moves a 50g 30 cal at 830 with an ES around 9.
First, I'll say the crown is a laser beam with no wind at 50 yards with the 25.4g pellets at 50 yards. It litterally makes a single hole in the paper as everyone claims. But the ES shows up at 75 yards. Using a chronograph, I can literally tell within 5 fps what the chrony reads from where the pellet hits the target.
So my process started with increasing the hammer spring to increase the velocity of the 34g to about 825 fps before further increasing the adjustment of the hammer spring no longer yeilded an increase in velocity. I then increased the regulator pressure to 130 bar and not much happened. It seemed that very little increase in velocity happened but ES went crazy. I was getting 823 one shot and 850 the next shot.
I then decided to test moving the reg to 140 bar to verify that I could move the pellet in the 860ish fps range and where would the hammer spring need to be set to accomplish that and what would that mean for group size and ES with the 34s?
So, today I did that and got that configuration worked out and the gun seems to like it as the group sizes are okay with a few fliers but ES measured at 22 during a 13 shot string. Verticle group size is smallerat 860 vs 830 at 75 yards. I'm pretty sure ES will be exagerated at 100 yards so I'm still concerned that I haven't found the sweet spot to get the ES down under 10. I'm worried that with the crown's lack of the valve adjustment, I may not be able to have confidence in the gun with this high ES condition.
Anyone else with a crown got the 34s figured out? I'm currently at 140 bar and 858fps average. Anyone else having high ES issues with the crown?
Here are a few groups for comparison on 1 in grid paper.
50 yard crown groups as advertised..
75 yard groups with 25.4s no wind.
75 yards with 34g at 860ish fps (notice how the groups grow vertically)
and considerably more fliers. These are my better groups from the 34s.
...Still in search of the sweet spot.
I think I will also follow the prior suggestion and move down the regulator and start at about 130 bar and sneak up the hammer spring a little at a time and measure ES through the range of hammer spring tensions. Move up 5 bar and do it again and see if I can find a spot with low ES and an acceptable velocity and hope the gun likes it.
Any input is welcome. Hope this helps someone out.