.404 HDS Basic
0.5390 rim
0.5420 base
I quote "the demensions of the rim,base and length of this basic case are almost certain to be slightly different from the corresponding MAXIMUM dimensions specified for any case you plan to form from this one. Don't let the normal variation of a few ten-thousandths of an inch -- even a few thousandths -- worry you."
This is out of Ken Howell's "design and forming CUSTOM CARTRIDGES for rifles and handguns"
Does this help. This new Ruger case has the same rim size as the 375 H&H with the base the same size as the belt of the H&H case.
Jim
Alberta