Rick, From what I'm able to surmise, this would have been a medium caliber fuze, use in 4", 5" and possibly 6" common rounds. The main charge for those rounds were either black powder or a combination of black powder and TNT, so the "magazine" would have been full of black powder also. I've been trying to get more info, collecting bits and pieces here and there and trying to develop a picture, but the pubs for ordnance from the 1870's-1930's is almost non-existent. This one appears to be an experimental fuze that made it to service status and is the non-tracer version of another service fuze that I will post later. Cheers, Y'all, Bruce.