I do have a 505 Gibbs, so much me being practical. My choice is based on tradition and just liking the Gibbs and CZ offering one. Now, the question was: why someone would choose a 416/50. I have no idea what that is or how it head spaces. This question posed with an inference that the 500J was better. Assuming 416/50 works, I can see there would be some advantages. Not short, fat and rebated or enormously large like the 505 Gibbs. Another modern choice is the 500 A square. There are advantages which could be debated by reasonable gun nuts. And, I think it fair to point out that 500J is far from prefect, past or present.

I believe all 24 original 500J rifles built by Jeffery were single column magazine holding only 2 rounds. That is one way to get good feeding. The Schuler was, I believe, a slightly dimensionally different round. That difference in brass may have been yet another issue in the past.

We can love our 505 or 500J but have to admit advantages can be found in some modern alternatives. If that is what a guy wants. I don't want one, sounds like at least two others here feel the same. I do like and want a 585 Hubel and as Ash said there is no traditional option there.