Thanks all for the replies, seems we're on a roll here.

500Nitro, thanks for that, I was thinking 2218 and 2225 would have been better suited to the job. Also this will be a full build from scratch so slugging the bore is not a worry. I am planning to build it on a 6mm/.243 barrel as mentioned by Simonsaorsa in the article he has, thats the reason for wanting to use 115gr projectiles.
I have reamers, forming dies and loading dies sorted and its just a matter of finding the data to get this thing going.

Simonsaorsa, I've been looking for that article for a long time now, I'd heard of it but could never quite get my hands on it so a PM will be on it's way shortly.

Red