My Carcano is the most inaccurate rifle in my collection. It's a M38 calavary carbine. Short barrel, fixed sights, 6.5 mm caliber, folding bayonet.
I've shot original miltary ammo through it as well as reloads made from mannlicher shoenaur (SP?) brass.
What I've read said that the gain twist rifling was abandoned on rifles made in WWII since it did little if anything to increase accuracy, but greatly complicated manufacture.