My S400 really benefitted from a silencer (AA silencer) it tightened up the groups really well.
When I bought my Steyr LG100 it had a muzzle brake on it. When I removed it, the groups tightened up.
Steyr say there should be nothing on the barrel as the gun is finely tuned and adding anything ruins the tuning.
Anschutz 2013 MEC1 .22LR
Miroku 3800 12bore