Good info, and an interesting project. As I'm sure you well know, but perhaps casual readers might overlook, all real ammo has to be stashed away and reloading sessions have to be meaningful, focused, and, when over, they are OVER. Shotgun goes back where it goes, reloaded with your typical ammunition, or unloaded completely if that is how you store it, and the training mode is switched OFF.
I have heard of a single negligent discharge story in Washington State with a Mossberg 500 blowing a hole in the floor... I am sure there are others.
Personally, I use the commonly available 12-ga. snap caps because they wear for a very long time and repeated use. They look pretty beat up these days, but they still work OK. I like the idea of making a more proximate size and weight. I guess I'm inclined to ask you how the brass case heads will hold up to repeated practice loadings? Interesting DIY, thanks for posting it.
