Anyone happen to know the bore and groove diameter of CZ factory barrels in this caliber? Thinking of ordering the RCBS bullet mould and would like to be sure.
Thanks if you can help.

Get a .418. .002 over groove diameter.

Bill,

The .375 H&H, .416 Rigby, and .458 WinMag barrels on the CZ 550 Magnum come from Czechoslovakia, and are done to C.I.P. standards. They are all on the same contour, about a number 4 sporter.
That is about perfect for a .416 Rigby, a little heavy for a .375, a little light for a .458, overall a good compromise.

I cannot recall slugging any of the many .416 Rigby CZ 550 barrels that have been through my hands, but they all performed as expected and I had no reason to doubt their C.I.P. specs:

bore: 10.36mm = 0.4079": .408"
groove: 10.57mm = 0.4161": .416"
twist: 420.00mm = 16.54": 1:16.5"

I have checked twist and found 16.5", expect the bore and groove to be the same as above.
Trust but verify.

So, if you do a throat slug to fit a custom-designed bullet mould to it (a' la LBT), you will get some of the rifling to measure also.
The throat is a zero-parallel-sided free-bore, just leade, by C.I.P. standards:

Tom, RIP, thanks for the thoughts gentlemen!