I have a HW100 in 177 and improved accuracy significantly by:
1. Free floating the barrel, you can do this simply by removing the rubber ring on the inside of the A frame.
2. Putting a rowan engineering air splitter on the front of the barrel. Play around with the insert to fine tune the accuracy. Start with around 4mm in front of the body of the splitter
Accuracy at 45 yds improved from 40mm to 15mm.
I did the same with my Steyr LG100 and got similar results.