The Mk3 gun bushings were also riveted and soft soldered. It makes it fairly easy to get the bushings out if you need to. That’s the only reason I can think of for using soft solder.

One of my Lanchester magazines came apart recently. It wasn’t the usual failure where the retaining plate flies off into the grass never to be seen again… followed by the spring and platform. This time the reinforcing sheath stayed in the magazine housing and only the body came out. It turns out the reinforcing sheath was only held on with soft solder and not spot welded like others are.