Jagermeister - Re-read the Max quote below ... he's not talking about the 21, already confirmed that the 21 barrel lug is solid.
I also recently acquired a English SxS. First time out with this gun & there was not doubt that the forend was about to fall off due to a very loose barrel lug. The gunsmith resoldered the lug and now the forend has a snug fit. My concern is that when the barrels are moved side to side, you can hear some of what I assume is metal rolling back & forth between the barrels. I also heard this prior to realizing that the lug was loose.