As the are not to be used as a suppressor so only need to withstand heat, the Airsoft ones work fine. They can easily be had in lengths from 120mm to 240mm and come threaded appropriately on one end. Simply ream the other end out enough to fit over the barrel, remove the foam material from inside and replace with fiberglass insulation if you want and a dab of loctite, thread it on and viola......you're done for the cost of about $20. I've made a few of these for my rifles and a couple for friends.