These are the best buckings i have seen around, they actually increased my Javelin AEG M4 on 10 FPS, may be because javelins come with the worst generic kind of bucking, but i also put the other one of these on my DBoys AK47 and improved 8-12 FPS, so it really works, its a tight cool piece, you might have to push it hard to get it inside the HopUP chamber.No need a pro technician for this. just dont lose any part or forget where they were before u started.