I've not been collecting them all that long, first one was when I was a kid, dad gave me an old H&R 12ga that was made in the 20s from all I can tell, next one was a 20ga Pardner in '91, no rifles until 2004, started with a .223 Ultra Varmint, then a .45-70, then a couple accessory barrels, .243 and .25-06, and ......
If you get a used Handi, make sure the frame serial number prefix is HN or NN or later, 1999 is the oldest they'll fit the .444 barrel to, the barrels listed on the acc barrel list that are marked with an *, mean they're high pressure calibers and they'll only fit them to frames made 1999 or later.
The .444 is one of em!!
Tim
http://hr1871.com/Support/accessoryProgram.aspx