Umarex HDX Muzzle Brake

thingiverse

This is obviously just an asthetic addon, as in case of regulatory <17J power (for PL), there is not much gases to have any effect. Still, if you want to have a bit different look of your HDX and this design catches your eye, print one and stand out from the crowd ;) This piece is held in place with two small 3mm screws and nuts - you should be able to figure it out looking at the designed recesses.