3sixbits,
The neck dimensions are tight enough that if one wanted to youcould certainly take a light cut on the case necks to true them up for concentricity purposes and still have a plenty tight enough chamber neck for great accuracy and little case neck wear.
The dies from Redding are the standard Full Length sizing dies which for big game hunting I highly recommend with these rounds as they are VERY minimum in body taper. I recommend partial full length sizing by setting up the sizing die to size only the first 2/3 to 3/4 of the case neck which will just slightly compress the body diameter of the case allowing effortless chambering without changing the case shoulder to chamber relationship at all for great accuracy and consistancy.
If my customers want a bushing style neck sizer I build those off from Redding Comp dies using the same reamer as used for the rifle chamber for a perfect fit. For the 270 ALlen Mag I would get a 7mm STW die and ream it out to the 270 Allen chamber so that it would accept the virgin 7mm RUM brass for sizing down the neck.
For the 257 and 6.5mm I would get a 338 Win Mag die and rechamber to the 257 and 6.5 chamber. This would allow the 338 RUM cases to be stepped down by using different size bushings.
I do not like the S type neck bushing dies as run outs are higher then I like fron the non supported case body.
I have actually found the standard FL die will produce much more consistant neck run outs when properly set up then the S dies on average. The Comp die is by far the best for getting match grade ammo but I consistant get ammo with neck and bullet run outs of less then 0.002" with standard Full Length dies and a custom Redding Comp bullet seating die.
On the Rem brass issue, people make a bigger deal out of it then there really is. Sure it is not held to the spec that Norma or Lapua brass is but it is 1/3 the price as well. With just a bit of bench time you can produce ammo that will run with any european brass around. Just takes a little time in prepping and sorting.
The groups I shoot at 500 and that at 930 yards were with once fired Rem Brass that were not even sorted only trimmed to length and loaded with quality tools for good run outs. This is the key to accuracy at long range, far more so then what brand of brass you use in my personal opinion, at least for an extreme range big game rifle. Comp may be a different story but I am not a comp shooter.
Good Shooting!!
Kirby Allen(50)