I have a Krag sporter with a later barrel that slugs a true .308 bore and .311 groove. Chamber is marginally tighter than the Springfield Armory's somewhat cavalier use of the micrometer. Throat is reasonably long and slugs at .311.
I rolled 150 gr FN (these were lubed Oregon Trail bullets that I de-lubed and sized to .308) and patched out to .312/.313 w/9lbs onion skin. Patch to just above cannelure. Lubed lightly with beeswax/vaseline/LLA. Shot over 25 grs IMR4198. Results were highly inaccurate. It looked like some may have even key-holed.
My guess is that the relatively short bullet and long throat combined to make the bullet somewhat unstable entering the bore. Any other thoughts or advice?