From ACOP 415:
415 Metal boxes, including ammunition boxes, are not suitable and must not be used. This is because, firstly while metal is fire resistant it also transmits heat very well and secondly, because the metal container adds additional containment that significantly increases the explosive power of the powder. It should be noted that the requirements in this paragraph replace guidance permitting the keeping of black powder in a lacquered or tinned iron or steel trunk or box contained in A guide to the Control of Explosives Regulations 1991.46
Seems like there is a lot of inconsistency in hoe the elo's interpret the requirements then.
INteresting, it was a while ago but he was more than happy with my ammo box bolted to the floor as long as the actual container I put the BP in and was carried in was wooden it was fine.
Aren't we getting into silly town if we start thinking about metal jail bar type setups like Arthur mentions later?
Maybe if we weaken the ammo box it would be better and not contain as well. I suspect 15kg of BP would contain rather well in a concrete cupboard and an ammo crate would be largely irrelevant if it went off.?!?!