If H&R is still using the USPS, good luck. A few years back I sent my BC in to have a .204 barrel fitted. It took the most convoluted route I have ever seen getting there and back. My rifle had a better vacation than I did!
It was worth the wait, though. I'm pretty sure the Crows around here can hear a .204 round sliding into the chamber! They respect the accuracy and devastation it delivers and give it a wide berth.