I tried some 7x57 and didnot have any luck at getting a good case.
I checked some of the win. brass that i formed and am getting around .006 run out on the necks this is with a redding 243 ai neck die. I will re adjust and see if it will reduce the run out. what run out are you getting or do you bother.

The 243AI will lose 10-12 thou when fire forming. Chambers are usually 2.055 to 2.065. My reamer cuts a chamber 2.072.

Don't know why the make them so long. The reamer specs call

for 2.055 (Clymer). I made a lot of brass from 6mm Rem and 7x57 Win Super-X. The 7x57 was the best brass but they don't make it any more.



With this brass you can make full advantage of the long neck if you fire form with filler instead of bullets. The 6mm and 7x57 will shorten 18 thou. So you trim the cases 15 thou longer than chamber length and jam the into the neck transition. The final trim is 5 thou shorter than chamber length.



If your chamber neck is on the large size. The 7x57 or 270 brass 2 will let you nicely outside neck ream for best concentricity and minimal radial clearance in the neck. This makes for long lasting brass and good accuracy.



I even made brass for a .281" chamber neck from 30-06 brass and ended up with .0015" radial clearance. Case neck walls were .017". That was a terrible chamber.



Look at my web page. You will also find a link to the 243AI loads page. Longneck 243AI