vudon, sorry must not gotten your email. Email me:
[email protected] to properly trouble shoot your BC;
1. Shroud removed --- just barrel and check for proper mounting---> take 5 six shot groups from 200 to 175b if regulated if not find the flattest string and take group accuracy @50y
speed setting with above testing;
current speed to around 20fps increments till max speed is reach,if possible around 925fps (most ST barrel like this speed and some don't like it slow)
2. Install a barrel that I know is accurate and take shot string with the same setting as above
if accuracy are similar with no issue then shroud reinstalled with end cap and take group accuracy as noted above and compare groups, install NC LDC and take group accuracy as noted above, look at all the groups and compare--most like you can pinpoint issue area.
your current groups are pretty decent -- there are so many variations to have that groups and many more to get it tighter.
notic your power wheel on #2, it should be set to the largest TP hole, with a smaller TP aperture accuracy always open up.