If you got the 5gal bucket route, cut a 10" plywood disc out to fit in the pail bottom and reinforce it. Then, assuming its a plastic one not a metal one with tabs, glue the top shut and duct tape around the joint. UPS charges extra for shipping this way or any way that's not covered in cardboard, such as a wooden crate. If you do make a wooden crate, cover the outside with cardboard so as to avoid this surcharge.
It is critical to wrap the projectile tightly in newspaper or towelling and not let it budge at all in the container. Any wiggling room and the heavy iron projectile will act as a battering ram inside your container and force its way out. Styrofoam peanuts are a major nemesis as they just smoosh down and create the dreaded wiggle room. Use lots of good shipping tape.
I have lost shipments with all the major shippers despite having photos and exact weights and dimensions of the projectiles. I probably use UPS Ground the most and so have lost the most things with them. Keep your total package weight under 150lbs or it becomes freight and the cost goes through the roof.
