The M21 can "fool" a unknown owner into thinking his gun is becoming loose- but in an homage to the British and their "assisted opening" feature found on certain Best guns as an option, the WRA design team added this to "assist" the opening of the breech when the lever is swung to the right of top tang center.
I have my late father's M21- a field grade 12 with SST and AE he bought used (owner traded it in on a browning 20 Superposed) in 1949-1950. It has 28" barrels and is choked imp. cyl. right barrel, imp. mod. left barrel, and is marked "3" chambers" on the left barrel side at the breech area- but it is a field grade, NOT a Heavy Duck M21. I only shoot 2&3/4" loads in it, and since Dad gave it to me in 1980, I have never changed the trigger selector button in the trigger blade. Nice guns, but a bit over-priced in today's secondary market, IMO.
The British sporting set, when using a matched pair of double guns and a loader, apparently felt that time was saved when the Gun- opened his shotgun, ejecting the fired shell(s) and passed it over to his loader for the loaded and closed second gun--Anyway, that's the reason for the spring in the barrel lug--
