Officially known as the 6.5 x 55 Swedish Mauser, the old "Swede" is, in my humble opinion, the king of the medium bores. Hugely popular here after WWII, coming into the country by the shipload along with the K98's, SMLE's, Springfields, Garands, and whatnot, the little M96 Swedish Mauser was the creme of the crop. The best made, the best finish, and a sweetheart of a caliber. I've had several over the years, and a couple of other rifles so chambered. My oldest son killed his first big game animals with a M70 Featherweight so chambered.
You folks are probably aware by now of my affinity for single shots and lever guns. The best (readily available) modern single shot, in my opinion, is the Ruger #1. Well, after years of looking, I was finally able to marry up one of my favorite calibers in one of my favorite rifles - I found a NIB #1A Light Sporter in 6.5 x 55. Ruger made a run of 200 of these about eight to ten years ago, and I missed getting one then. Well, I finally fixed that.
The reason I believe the 6.5 x 55 is the "king of the medium bores" can be summed up in two words: sectional density. The "standard" original military bullet weight was 160 grains. In such a small bore, that makes for one hell of a long bullet, which translates to very, very high sectional density. While many modern shooters have sought to "update" the ballistics of the old warhorse by dropping bullet weight to 120 to 140 grains and increasing velocity proportionately, I believe that is a mistake. It earned its stellar reputation in the field through straight, deep penetration, achieved with its 160 grain bullets at moderate velocity.
By way of comparison, here is the 160 grain 6.5 bullet flanked by a standard 50 grain .223 and 180 grain .30 caliber. Note the length of that 6.5:
Loaded rounds with the same bullets:
With a modern action like my son's M70 Featherweight, we can push these bullets a bit faster than the old rear-locking M96 Mausers would tolerate. Still nowhere near modern "magnum" velocities, but an honest 2450-2500 fps is well within the safe limits of a #1 or a M70. That's really all one needs to cleanly take deer, and even elk, if one chooses shots carefully - pretty much a prerequisite with a single shot anyway.
Anyway, I'm a happy guy. This is the ultimate rough terrain "mountain" rifle, or just general "woods bumming" rifle for me. It will never wear a scope, as such an appendage would ruin its balance, aesthetic, and ethos. I might put a peep on it, in deference to my aging eyes, but that's about as far as that will ever go.