The barrel on a Knick should not touch the forearm. The wood is held away from the barrel by the forearm iron so as to leave a generous gap, perhaps 1/32" between the barrel and the wood. The latch lever (part 62 on Dr. House's diagram) holds the iron to the barrel. Part 60 (latch escutcheon) dictates the barrel-wood-gap. All of this stuff is fixed - not adjustable. The forearm assembly (wood and iron) is held/pushed against the front of the receiver by the spring-loaded fore-end fastener (part 53). Four screws hold the fore-end iron to the wood, and if those are tight and the fore-end is still loose, it seems the problem would fall to the fore-end fastener bolt.