I'm using Alpha LRP 260 brass in my 243 Improved. Necks are a little thick, but still have .004 clearance. Loaded necks are .274-.275 OD, neck of my chamber is .279.
I went pretty far up in charge (51 grains) of H1000 with a 115 DTAC at 3085 fps in a 20" barrel. That load was definitely hot, but only showed a faint ejector mark. Primer pockets didn't show any growth in one firing. The final load is 47.7 at 2900 fps.
Either Alpha or Lapua LRP should be more than adequate for many firings.
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