The 6 Arc is a low pressure cartridge 52,000 I believe . This is due to its Grendel parent case design . The ar bolt is milled out and had problems with higher pressures . The answer was to lower pressure . That being said you are building a bolt gun . I see no advantage to the ar platform limitations for a bolt gun . Also the mag length restricts the oal with longer projectiles eating up powder column . I own a 6.5 Grendel in a psa ar And i love it . Great cartridge in that platform . To Max an arc potential in a bolt is to go way over pressure . In that case why not use a cartridge designed for the platform like the 6br family if cartridges . Unless you just like being different that's up to you .