I just brought back a press, dies, a lead melting furnace, mold handles, and s couple of bottles of bullet lube. Declaired it at customs - Ft. Erie Ontario. They asked me if I had any bullets, powder...and I cut them off with a smile and said.
"I am VERY aware of what our import regulations are, as well as the US export regulations and I've been VERY careful to make sure I'm not stepping on anyone's toes"
Reply was "Thank you sir and have a nice day" and we drove off.
Here's an easy way to remember it. If it is a gun, fits on a gun, or goes in a gun, you can't bring it back. Other than that, you're good. The only thing that goes IN a gun you CAN bring back is a cleaning rod. Bullet moulds, dies, gun cases, cleaning supplies...all good, no problems...yet.
I don't know if you want to be trying to bring that stuff on a plane though. You'll almost certainly be unpacking it to show them, checked or not. I got one of those "Department of Homeland Secruity has inspected your bag as per section ....blah blah blah. In the future, here are some tips on packing your bag....blah blah. I had my laptop buried dead center in my bag with clothes all around it, so they opened it to have a look I guess.