Dennis, since you are talking single shot, options are many.
With the politics of today, importation of brass could stop as we learned in the mid 80's with Sako brass.
So, any case that is based on a 22/250 or 243 case would work well for you.
A custom 243 may sound boring, but they are Extremely accurate, and as a hunter the AI has no down side.
Some years ago, I built two custom 6/250 AI's and the speed with the 70's was at 3800 out of a 28" barrel with win 760, with match accuracy. If you look at the design on the 6/250 AI, it is very similar to some of the new cartridges.
