my plan was to ream/trim the inside of the .308 brass after its been cut to length so the bullet will fit.. brass would be a tad thinner around the mouth than the rest of it but that shouldnt be a big issue, not for .006" difference, also it looks like this cartridge will probably be about 40,000 PSI as well since im basically going by .45 win mag specs.. theres really not enough case volume to shorten the case and increase pressure without saving at best a few millimeters over total length, plus if i did that it would put me at an akward magazine length
since i am going for the same COAL as a 5.56 cartridge, any action short enough for 5.56 should work fine, so long as i can put a 12mm bolt face on it, and there are a few AR-15 calibers that use magazines that should work well for this.. so, i can use front locking of a shorter action designed for .223 length cartridges
i'll need to add a .458 neck reamer to my tools when i start making brass for it