Last week while playing with the forearm on the 30 carbine barrel I discovered a little trick to make the fitting of the forearm consistant. With the O ring in place, I put a very short 1/4 20 set screw in the forearm lug hole. By adjusting it in and out you can make the forearm screw bottom out on it at any amount of O ring compression you like. Then just some blue locktight on it and every time you put the forearm on and tighten it down it will have exactly the same amount of ring compression and pressure on the barrel. Larry