Good morning men.
You must know that in Italy the only firearms - except for hunting shotgun and muzzleloading guns - we (Italian) can legally bought are those registered in the National Common Firearms Catalogue: any other firearm (hand or long gun)not enrolled in is to consider "war gun", consequently illegal. Among calibers Gary and wapitirod have mentioned only .357 Maximum and 500 Linebaugh are registered - so legal -, but if I'm not wrong only handguns able to shot Linebaugh .50 cartridges are Ruger custom revolvers (Gary Reeder, Bowen, etc.), and in Italy we would have to wait about 12-15 months before owning one; the .357 Max, instead, I have no interest in, it is too... "small".
As far as .500 Wyoming Express, I think that nobody (till now!) has worried about, while I'm sure that in Italy neither greatest gun expert know something about .500 JRH or .510 GNR (me yes, but I'm an exception... the exception proves the rules... what you say, I can consider myself an expert? ).

P.S. My english is worsened in the last month: too much little excercise! Sorry