I was brought a 94 Swede cavalry carbine that had an extremely rough bore. It would shoot the Lee cruise missile unsized, but with poor accuracy. Jacketed .284" bullets would not stay on a target more than 15 yards away, and even there some of them keyholed. I bought a box of Hornady 160 grain .267" bullets for the Carcano, and tried them. I blew a couple of primers until I seated the bullets far enough off the rifling, and then it would keep them in four or five inches at 68 yards. I decided there was nothing to lose by fire lapping it.
In order to get the cruise missiles to chamber, I shortened the neck of my five lapping cases until the boolits would chamber seated backwards. I fired 15 with 240 grit, and ten each with 600 and 1000 grit, cleaning after every five rounds with several Kroil-soaked patches, brushing, more Kroil patches, and finishing with JB bore paste and Kroil patches. (Fortunately I bought a gallon of Kroil some time back.)
The bore now looks shiny, and I can seat the .267 bullets to a reasonable length. The bore slugs .267 at the muzzle, which is the tightest point. With the Carcano bullets about .120" off the rifling, I got about 1750 fps with 29 grains of H4831sc. Five-shot groups at 68 yards were 3" or a little better with the iron sights. I am going to try to work up to at least 2000 fps, as the owner of the rifle wants to use it as a deer rifle in the brush.
It occurs to me that it might also be possible to lap corroded .308 barrels out to accept .312 bullets as well. Chamber necks might have to be reamed to do that. With the drying up of 1903 Springfield barrels, that might resuscitate some rifles.