Casper,
My 416 Taylor rifle is a 24" barreled syn stocked rifle with all metal cerakoted, an all weather, all game anywhere rifle, it wears a 1.5-5 Leupold in steel Talleys also cerakoted and drilled for 8-40 threads.
It has a British crown on the 98 Mauser action with no other marking other than the bottom metal marked Parker-Hale, with that in mind i knew it was of modern steel, so safe and plenty strong for max load search, I also didn't care for the limited available load data and powders used decades ago.
I looked the case over as powder column relates to neck size, then studied powder burn rate charts, with a bit of extrapolation, I picked CFE-223 powder, extremely dense well packing powder, flat safe pressure curve, plus it helps clean the copper fouling from your bore.
I worked up to a safe 77.5grs of CFE-223 under all manner of 400gr bullets, 400gr Hornady round nose softs and solids, as well as 400gr partitions, all bullets get a firm roll crimp from the Redding dies, FED-215 primers used throughout load development.
Brass used is A-Square, Jamison, Quality Cartridge and first annealed, then ran into a set of 358 Norma mag dies, the necked on up to 416 with the Redding dies WW-Super 338 WM brass, the necked up 338 WM brass is short, but mighty fine for practice shooting with the cheaper Hornady bullets.
Even with all brass makes, with the first three being proper head stamped cases, the velocities were never more than 20 fps e.s.....................all loads average a true 2409 fps, that's exactly what I was after with this project, primer pockets remain tight, easy load and extraction, a real powerhouse load in a very effective chambering.
Start at 74gr CFE-223 under 400gr bullets and work up.