Paul- that's quite a round - ending up with 85gr. capacity from a 'standard' case.

NitroX's question about headspacing is a normal one- which started many years ago by people who didn't understand headspace or properly setting their dies.

Lyman is to blame somewhat as in the older books, ie: 44 and certainly as late as the #45 I purchased back in the late 60's when I started handloading, make mention of touching the shell holder to the bottom of the die. Today, we know this moves the shoulder back- in varying amounts according to the minimum and maximum tollerances of the die maker. The shorter 'chambers' inside the dies, move the shoulder more than the longer ones - stands to reason.

Paul - your annalogy of the .458 mag brass is a good one and holds for all straight cased magnums, including the much newer .458 Lott.

The monimal case head size of a normal short or long mag. is listed as being .513". Some ctgs. like the .350 Rem Mag are normally a bit less- sometimes. Brass mfgr's also have minimum and maximum tolerances.

I use a tapered expander for opening up .30/06 and .270's as well as .35 Whelens out straight, then neck them down to a crush fit. This works for me and if using new brass, 100% success.

Here's a .300 Win MAg necked up and holding a 400gr. case bullet of .416" diameter. I turned off the belt and reduced the rim to fit a standard .473" bolt.

Here's my process for making .375'06IMP's. The two loaded rounds are 270gr. TSX @ 2,650fps (not max) and a 300gr. Hornady Interbond at 2,474fps, also, a tich less than maximum - but plenty good enough.

Here's my expander dies for opening up 8mm and .30'06 brass straight.