The Danish Madsen firm (Dansk Industri Syndikat) just never quite hit the big-time. They built lots of interesting, good firearms, but never quite came up with something that became really iconic. The M/50 is a good example of this track record – it was functionally a pretty ordinary open-bolt submachine gun, but had some innovative features. The receiver – including magazine well and grip – was made from two large pressings, which were hinged together at the back and held together by the barrel nut.
Certainly makes for easy maintenance. Doesn’t leave much to salvage when they’re chopped up as parts kits for US import, though. They sold reasonably well, but never really took off.
Madsen M/50 SMG Handbook (English)