Sir Larry,
That is optimum for the .458 WM+ with 404 SH,
3.370" with 2.490" brass length
or 3.380" with 2.500" brass length.

The FN Mauser with Sunny Hill mag box
was found to feed well from the right side of box
but problems on the left side of box ...
a minor delay in completion to correct this.
Gunsmith will work his magic on the Mauser feed rails.

Ron aka "Rip" for Riflecrank Internationale Permanente
NRA Life Benefactor and Beneficiary
.458 Winchester Magnum, Magnanimous in Victory
THE WALKING DEAD does so remind me of Democrap voters. Donkeypox.