Helo - I have a Yankee Hill Machine light weight 4-rail forearm on my bushmaster. There is some play (the forearm rotates slightly) in the forearm. I purchased a forearm wrench, and was advised by YHM to dissasemble the forearm down to the barrel nut and realign it with the next available gas tube hole.
I am relatively new to the AR and wanted some advice on doing this. Sounds realtively simple, but wanted to check before I started.