What's the policy on shipping fake ammunition in the USPS?

I produced a number of "dummy" rounds of rifle ammunition for a friend, They are totally deactivated, however at first glance they do resemble real ammo. He lives far away and I would like to ship them to him. Would I run into trouble when the USPS x-rays them? Would UPS be better? A label on the inside/outside explaining the contents. I really do not want to lose these especially when they aren't even hazardous.