Does anyone know either:

A: has anyone used 338 Lapua Mag cases necked up to 416 to "recreate" the 416 rigby with a higher max pressure
OR
B: Where one can obtain stronger, custom Rigby brass with a thicker web and sidewall that can take 58,000-65,000PSI?

Don't know where you can get such a thing. Also can't imagine why you'd want it. A 400 gr TBBC at 2550 fps is all you'll every need.

Why? Becuase I can-maybe.
That sounds a bit hot for the old beast. Is that out of the Speer manual?

The LM brass has a case length of 2.71, while the Rigby is 2.90. Where you gonns get the extra .19 length from??

Now, you might be able to start with 416 Wound-a-beast cases and turn off the belt......

Or do what I did, and buy new .416 Hornady cases

Yeah, I remembered the case length difference after I posted, but I can just have a custom reamer and dies made. I thought about using the Weatherby, but the rim dia. is slightly smaller, and the brass is even more expensive than 338 LM.

And Ian, aren't the Hornady cases still only rated to the same SAAMI spec for the Rigby (47,137 PSI)?