A friend has done a lot of long range shooting, and has built several rifles for that. What he has discovered is that for fine accuracy it seems that the bullets can only be driven so fast, and that the regular 6mm Remington case will easily get there. He has also demonstrated that full cases give better ESs. This might be something that you should keep in mind for your project. Sometimes bigger and faster are not better, at least when it comes to top accuracy. What he has run into is that too much pressure on long bullets can cause barrels to copper foul and at that point they stop shooting until they are cleaned. He has been all about high BCs and velocities but has learned that there are practical limits if one wants to be able to shoot long strings without having to stop and clean while in the field.