I'll throw one out there that gets you good vel a great neck decent shoulder angle. 6 SLR. .243 case one trip thru a SLR die and you get a .321 neck 30 degree shoulder same oal as a .243. Brass is way way easy to find and no more prep than a parnet case. Lapua Norma Peterson RWS Winchester, Hornady yada yada yada. Not only will you find it a local store you likely can find it on the ground or in the trash as most any range lol. Do not forget while more powder can mean shorter throat life there is no one making a person run that hot where in a small case its all shes got. 115 @ 3k not an issue and not @ heavy pressure. Likely allow for using h1000 with its cooler temp flame which combined with the neck length and shoulder angle would likely get you vel, accuracy, less throat wear. Basically its the xc meets the 243 and best of all its not a creedmor.
Could you expand on "best of all its not a creedmoor"