I've got one, I bought Mac's 6mmAI Hornady hydraulic form die and the matching reamer from him, I sent it, my thumbhole 243 Ultra barrel and my Optima Elite 243 barrel to Wayne York along with the reamer and had him rechamber both to 6mm AI in trade for the reamer, he finished them up and returned them to me in less than a month which I thought was excellent. RL19 under an 87gr Vmax runs about 3300fps for both of the 24" barrels, accuracy was more than acceptable, I think with a little forend work the Ultra would shoot bug holes, haven't shot it since tho.
Tim
