Historically speaking, and notwithstanding
BenKK's positive experience with the Sako, the .500 Jeffery suffered very problematic feeding in the
standard length and
standard width K98 Mauser military action, on which rifles were built in England when Rigby had exclusive rights to the magnum length actions.
These feeding problems were such that most British gun makers ended up building single stack magazines for the .500 Jeffery. This either resulted in a 3 round rifle (including one in the chamber), or a very long and unsightly (in the period's thinking) magazine extension in front of the trigger guard.
These issues are resolved in longer and wider (width is the most important issue) actions than the standard K98 Mauser (e.g. Sako, CZ 550, etc.) but the .500 Jeff remains a rebated rim cartridge for which it will always be more difficult (read time-consuming, read expensive) to fine-tune the feeding.
From another perspective, now that the affordable and cavernous CZ 550 magnum action is out of production, and will soon dry out off the market, I expect that darn few gunsmiths will take the pain to build .505 Gibbs rifles on available actions (the Win 70 action and clones come to mind), so the .500 Jeff may by default regain prominence as the .505 will become again a very expensive proposition on .416-length magnum Mauser actions, or Granite Mountain Arms and similar custom actions...