For big long cases our testing is showing that the 416 easier to get powders to work with, less problems ..
Maybe building a target gun,don't have 375 barrel all ready, maybe go 416....

We got cases, 416 HE and 416 HSM, as well as 375...
CEB and others will have bullets...CEB will be doing .416 in 450gr, 475gr, 500gr, 525gr and 550gr

Got sent 5 thick sided sample cases, same OD base as 585/375.416 cases, same belt, just .180" longer,
did a 416 HE, chambered extra barrel , cases stick over 50k. They have about .042" total taper, .021" per
side, when I necked couple to 416. That is a lot of taper , twice the taper of my 416HE...hanging up at 50k..

I could maybe go to 65k with these if we made taper with ..012" - .016" more taper to each side, but that is
no way to build target cases. I'd have to crunch down case shoulder diameter. And would look like 30-30.

And crazy part is, the case has enough brass material to thin up sides and stretch them way out to 4 or
more inches,, They weigh 150 gr more than our 585/375/416,, but with real thick sides they actually
hold less than our 416 HE with thin sides, that is .180" shorter...Our case does 65k ok without sticking..

And we can make super long 4" cases work if we had means to get them built, as we have
15 powders slower than HBMG.Here is pic of thin and thick sided cases, sectioned for comparison.Ed..