Re: 6.5 Arch
6.5 arch and 6 Arch are made on 6.5x55 case this cartridge is an improved "a la gibbs " with the shoulder moove to get a longer body and a shorter neck
this cartridge is near the max you can get as improved on 6.5x55
If you plan to go with Arch check chamber base diameter , usual 6.5x55 chamber are broad and not hold case base for hight pressure load .
performance will be close to the 6.5/284 but with available case in 6.5/284 you can escape to the pain of forming the Arch and ger ready 6.5/284 case , no custom set of dies ...