Yes, do install the plug before inletting the tang. Before you install the plug though darken the rear of the barrel, place it in the barrel channel, and give the muzzle a solid tap to the rear. You need solid contact, metal to wood, at the rear of the barrel inlet.
You will want the tang curved to follow the wrist as much as it will, you can do this before or after you install the plug, but before inletting. I also give the face of the plug a good polish, and the bore a good cleaning before that last plug install. use moly grease on the threads, a little dab will do you. I use these little gray packets of Permatex high temp brake disc lube for plug threads, you can get them at the auto store.
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