Max - I once had a pair of first year 21s and the forend was loose on one .The one that was tight was tight on either gun .When I compared them I found that the forearm retainer was bent on the the loose one . To fix this all I did was remove the wood turn the iron top side down and hit the retainer with a hammer which made it longer which tightened the forend up .

Please let us know if this works .Its very simple and works .I have seen it done many times .

AC