THere are a couple legal ways to do it, if declared, yada yada.
I personally ship using USPS flat rate boxes, very well wrapped in bubble wrap and peanuts. Super firm packing. NO problems.
My business ships out thousands of gel caps filled with fertilzer(for aquarium use) every month and usps doesn't look twice. It has to look odd.... Usually have a case of them in my car and have been pulled over with them in there, hard to explain.... but I've got a card, a website and normally wear a uniform(paramedic) too, so I can get by.
If you aren't trying to ship kegs or the like, I doubt anything will ever happen.