Dear Toot. Horn has ideal propertys to keep powder in, its light or best if light .Is strong, waterproof and will about melt before its destroyed by heat and it sits by your side left or right according to its natural shape & how the user prefers it .These particular Moroccan region horns are from cattle that don't twist noticeably the caps are usually iron or brass the size I think suites them as a magazine &' field use' ( Read mountains & desert but they do have fields ) The only ones from that region Iv.e seen had the cast brass horns genarally a bit smaller . their origin and dates I don't know but there where many . .Any copper or brass flask seem to follow the earlier pressed Lant horn shapes , pear shape mostly but all sorts of novel materials got used Tortoise shell , Camel scrotums, Sea shells ! ect ect according to whims or practalitys .. That's quite a dissertation . Iv'e left out Stag horns most species shed annually but Chital or Axis deer shed bi annually so the center isn't pithy but just a small vain hole . No good for powder horns but esteemed by cutlers for' Best' carveing or large knives like Bowies .
I once worked in a garage that had had a fire , On the wall was a powder horn full of gunpowder the heat had melted the horn so you could see the powder grains .Now that's some heat ! yet it hadn't blown up .That's one deservedly lucky fireman.
I say garage, it was more a workshop who keeps cars in a garage anyway !
Regards Rudyard