I just received my STX barrel kit for my Impact and noticed there’s no cavity for the barrel set screw. How does the barrel stay in the Impact securely?
The Thumb screw is shaped to go into the divot. It has a rounded end. The grub screw has a edge on it and as Ernest showed it slightly cuts into the stainless collar on the barrel. It doesn’t need to be as tight and doesn’t move. It was introduced by FX to overcome the problem of the thumb screw backing out."EliteAirgunr"The grub screw only allows you to tighten
it more than you could with thumb screen and at that point it is overkill. Thumb screw is completely fine to use. If you didn't have any trouble with it backing out before the stx barrel, you won't have have any troubles now.