I too am having a 500 Jeff. built, on a Whitworth Mauser that was originally a 300 Weatherby.

I notice that everyone here seems to going with the .510 bullets, instead of the .508.

Is there a reason for that, outside of bullet availability?

I thought most original Jefferys were .508 bores.

Regards,
Garrett

N Garret

you have a pm

Current CIP says .500" / .510" bore and groove with a 1:20" twist.
See here.