I have a 6mmRemAI Ultra, have only shot it one day tho, 87gr Vmax over Rl19 for about 3300fps. I'm using Hornady custom dies, bought em from Mac a couple years ago, also have a Hornady hydraulic forming die so I don't really have to fire form. Mac also had a custom reamer made to the same specs as the dies, I traded the reamer to site sponsor Wayne York of Oregunsmithing for rechambering two of my rifles, the 243 Ultra and a 243 Optima Elite, both seem to shoot real well, but I need another range day to refine the loads. I think a carbide reamer is required to ream dies, dunno if most smiths would have that to make matching dies or if they're even necessary.
Tim