I doubt you would need one specially made of brass for study purposes, when you could simply take a standard one off the assembly line....Just saying, BodesIt looks like the rotating bands were removed (the lip near the bottom). 105s wouldn’t have a base fuze, just a nose fuze. If there is a rear cavity, you’ll see female threads or shear pin holes for a base ejecting payload (usually illumination or smoke rounds). Extended range rounds could have a small cavity for what’s called a “base bleed” charge that produces gasses to reduce drag in flight. From these pictures, I doubt it’s any of those.
As for a brass 105, I couldn’t tell you what it was used for but I’d bet a 6 pack it was for some R&D or logistics purpose.
What fuze is in the nose? One looks like a solid shape and the other looks like a replica mech time fuze.
I see you picked up your Krag! Haha!