Tuning FX Wildcat MKI Accuracy Issue - Progress

[BradCO]

Looking for some FX WIldcat advice/suggestions from the crowd. I have a a FX WC MKI, 22 cal, which was bought new a few years back and it has been a great shooter, with JSB's 15 and 18gr, until recently. The gun started leaking around the valve seat o-ring, so I thought not a big deal. Ordered up the parts and resealed and thought I was back in business.

Now I can not get the gun to group worth anything close to where it was. Shooting at 23yds I get vertically stair-stepped stringing. Changed scoped, rings, etc. Re-tightening everything with zero pressure and at max reservoir pressure. Cleaned barrel, check pellet seating depth. Tried a few velocities from 920 down. Tried JSB's 15 / 18's and 15 Hades.

Currently with groups of 8-10 shots it's running AVG=880FPS, Spread=10FPS, SD=4.

I'm beating my head against the wall. Barrel crown? Other item that may have been disturbed when resealing?

These are groups at 23 yds with a 1 inch target. I do not remember being that bad of a shot

Any areas of wisdom to look further into. Thanks - Brad

 

[Strobing_NYC]

Pellet probe length? Should be 26-27mm

 

[GRITCH]

Have you replaced the breach seal o-ring?

Check your regulator pressure (should be 125Bar to 140Bar)

Check your shot string velocities for consistency to determine if your have regulator creep

 

[BradCO]

Thanks for all the suggestions so far. Quick update.

Strobing_NYC - I haven't measured the probe length as it's the fixed pellet style probe. I have verified the pellet is being seated past the barrel transfer port as to not deform the pellet skirt during firing. I've adjusted the pellet seating depth from max permissible and then back off to see if there was a difference. Also, verify centering of the pellet probe port to the block transfer port. No change.

GRITCH - Replaced the Breech oring and even replaced the barrel OD to mounting block centering orings as a swing for the fence. Reg pressure have not changed of been adjusted during the rebuild and the reg was not disassembled. I've tried different velocity of the 15gr pellets from 880 to 930 FPS. Currently running 900 FPS with a +- 4 FPS spread over 10 shots. I don't think this shows reg creep as it does not seem to bad.

Thanks - b

 

[GRITCH]

"" I've tried different velocity of the 15gr pellets from 880 to 930 FPS ""

The FPS range is hot for a 15gr pellet shot from a 500mm barrel. I assume the Regulator Pressure is unknown which is required as a baseline for adjustments.. Is the Hammer Spring adjustment cranked down or backed off? If it is cranked down then the hammer is likely hitting the valve too hard. Try this: Drop the FPS to ~790 by decreasing the hammer spring tension...then increase tension/FPS to achieve accuracy. I have a FX WC MKI .22 shooting JSP Jumbo Heavy 18.13gr @ 820 FPS's that is nearly hole-in-hole at 25 yards.



FX Wildcat MKIII Reassembly - FX Masterclass (Pellet probe length measurement procedure begins at 11:56)

https://www.youtube.com/watch?v=kQ4i0pIT1KM

 

[BradCO]

Process made.... After replacing and disassembling and re-assembling key components again with no change in the results I started eliminating parts. The shot string patterns are so consistent and repeatable that it seems maybe harmonics, etc. Changes the pellet speed, tried bedding the stock, probe position, etc. with no change. I had the LDC off the barrel multiple times to verify no damage to the crown. No apparent strike marks on baffles, and everything looked centered.

Then.... Decided to shoot a group without LDC to see if it changed harmonics and to my amazing the stair stepping stopped, but boy is it loud as I forgot how loud they can be without an LDC. Being this is first if the first gen Wildcat's it needed a custom LDC with Neil Claugue made years ago as it only has the M27 Thread for the FX stackable baffles. I tracked down a M27 to 1/2" adapter and was able to test with a DFL Tatsu and ZeroDB LDC, and the groups tighten up significantly.

The NC LDC has been on the gun since day one and seen many tins of pellets with no issue, but I wonder if an internal baffle has shifted to point it's not directly making pellet contact but enough to cause turbulence and create the grouping pattern at 25 yds. Maybe it took a hit during the rebuild, a pellet strike, etc. Or maybe still a harmonics things but I have two others that show no issue now. Unfortunately the NC LDC is unable to be disassembled, but I'm going down this path tp try to identify what 'changed'.

Interesting, to say the least.... -b

 

[GRITCH]

Looking at your target there is still vertical stair-stepped stringing

 

[BradCO]

GRITCH - Good catch, as it might of been me and the gun. Still running the DFL Tatsu, dialed up the velocity to 905-910FPS and took my time at the bench. This is a 8 shot group then a 6 shoot group at 23yds shooting 15gr Hades. Seems to be getting better, still will play around some more. Thanks for all advice. -b