So, basically all you do is take a .300 Win. Mag. & neck it down to a .284 bullet....correct?
Judging by the picture, it almost seemed that there were 2 "necks" in the casing? The standard neck...then another one (much shorter than the first), near where crest (where the projectile enters)?
Or is merely an optical illusion, from where the neck is crimped to the bullet?
Just call Dave Kiff at PTG and order a reamer. Then your smith can ream an existing 7mm rem mag seating die with the Finish reamer. Have a sizing die made with the roughing reamer and you are good to go with fire forming. Do not use the "penciled in" neck dimensions unless you want to turn the necks (I used Lapua Brass 300 win mag as the parent) then fire-form with 3/4 full case charge of bullseye no bullet of course and you are ready to go.. What you are seeing is the drawing used to make the reamer. Compare the body taper to a 300 win and you will see that it is less also the neck is shorter and at a 35% angle. Picks up almost 6% over the parent and the cases do not streach much.
Little rifle is the most accurate sporter save my 6.5x284 that is cut with the match reamer I use for my 1K BR rifles and that one is a tossup on some days.
Hopefully it will get a chance at a B&C Buck this weekend!! We will see..