Is Winchester still making the M-70 Fwt. in 6.5mm? Does Ruger chamber it in the M-77?
The 6.5X55 in modern loads is noticeably hotter than the old 6.5X54mm Mannlicher-Schoenauer that killed so much game in Africa in the early 20th Century.
Peter Hortberger, who owns Fallkniven Knives in Sweden, uses a 6.5mm on moose (alg), but bought a 9.3X62mm because he sees bears where he hunts.
His knives are exceptional, BTW. Not cheap, but superb. His Northern Lights line looks a lot like Randalls, but have modern laminated steel blades, with VG-10 cores.
www.fallkniven.com He has a few US dealers. Prices on the site are in Swedish kroner.
What concerns me about using lighter bullets in 6.5mm is that the leap to the rifling is farther than with 140 grainers, and Jack O'Connor said that using 139 grainers in a 7X57mm throated for 175 grainers caused excessive bore erosion. That's a big reason why he switched to the .270, which he championed so heavily through most of his gun-writing career. Still he got one of the last pre-'64 M-70's chambered in 7mm and one was also his wife's primary hunting rifle. I'm guessing that the old Swedish military rifles would be more affected by using lighter bullets, due to softer steels and the throating being for heavier bullets. The Mannlicher was known for deep penetration with 160 grain bullets, so I guess they can be used in 6.5X55, too. But I think I'd sight-in with 140 grainers, probably Noslers, if they're available in factory ammo in that caliber.