Re: 6.5 saum?
I was shooting a .300 RSAUM in 1k matches around a few States and Raton for about two years; to the point; I shot next to a guy in several matches that started using a 6.5 SAUM based on the .300/7mm RSAUM... Man... that thing could shoot! With that said... I had a 6.5 Rem Mag for years; it was nothing more than a little more powder 6.5 SAUM with a belt and far ahead of it's time as a Remington cartridge in the 60’s... Today'..., with all the good 6.5mm bullets and powders, I think I'd go with the “6.5 Rem Mag” if I was going to build "one more" short magnum; a very impressive and over looked cartridge which was introduce in the wrong rifle the M600
As for 6.5 SAUM reamers; you might try HTG George Vais in Boise ID
Barrel length; 26" for hunting, 30" for LR matches. And use a long action even though you could use a short, the long let's you use the long bullets in the magazine.