I know there's brass available but extra fat chambers have been common .
Also I don't mind forming brass when I have stuff I'm not using.
Enter the 6.5 Arisaka 1927 Type 38 Carbine that Dad left . There were a couple boxes of Norma but the barrel is closer to .271 than .268 , so that's where that kind of runs out .
A fellow suggested 243 which works but it needs to be trimmed and the few I did needed to be reamed . The easy 35 Rem didn't help as the extractor didn't hold the rim well enough to be reliable.
Time passes and I've had plenty of projects to work on .
I picked up a few 6.5 CM . Oh the blissful irony of the 1891 cartridge that is only 200 fps and 12kpsi behind the be all 2012ish 6.5CM wonder cart being formed from the CM . Yes , I did it .
In the Big Max it's a one pass deal once the size die gets lubed . I had to lube and size the top half then relube and finish. On of the bright spots is that the form bulge ends up mostly in the CMs generous extractor groove instead of a1/10" wide just above it like 243 did .
The body taper applied pushes the neck and shoulder forward vs pushing them back . There's no neck donut to ream because the neck doesn't change length or dia . The taper being added and body reduction moved the 1x 1.915 CM cases out to 1.980 formed for the 1.984 desired 6.5×50 length . There's no trim needed and just a minor clean up right at the extractor groove. A little bonus here the head is exactly right for the chamber .
The last happy place is that the headstamp is closer being a 6.5 than several other conversions and it won't chamber in the original chamber . Even if some ham fisted gorilla manages to get it in a CM chamber there's no risk of over pressure with the Japanese being only loaded to 50kpsi max where the CM goes 60.2kpsi .