RE: .257 weatherby
The following is a 1/2 MOA load for my Rem 700 LSS .257 Wby. 71gr IMR-7828, 100 grain Barnes Tipped TSX bullet, seated to max COAL (the number slips my mind right now), lit by a CCI benchrest magnum primer.
As for brass, you're on your own there. The little brass I have I had to make from both 270 Wby and 7mm Rem Mag. Actual 257 Wby headstamped brass is very hard to come by these days. I'd suggest that you make your own, either by buying 270 Wby brass and necking down (a one step operation with just your 257 FL die), which make perfect 257 Wby brass. Or you can make some with 7mm Rem Mag brass (this is the budget way to do it). Just run NEW 7mm Rem Mag cases through your FL sizer die using Imperial Sizing Wax on the neck and shoulder to prevent crushing. My success rate was 98%, with one case in 50 getting the shoulder creased. The 7mm Mag brass forms the neck and a partially radiused shoulder, but the full Wby double radius isn't formed by the die. The next step is just load them up with about a 5% reduced charge (I used 67 grains IMR-7828 for fireforming with the 100 gr TTSX bullets). After firing the rounds come out as sharply formed 257 Wby cases with slightly shorter necks than the Wby brass, which really isn't a big deal. I've gotten just under 1" groups average with these fireform loads, but the Roy likes it better when I push them harder to the 71 grain mark, where it really starts to shine.
Mike