.22 Hornet? .222 Rem? .222 Rem Mag? The .222 Rem was the most popular chambering for that short L46 action, I believe, and the CIP rifling standard for that is 356 mm (14") pitch, same as the U.S. But the best bet is to measure it yourself with a dry patch on a cleaning rod that you put a registration mark on with a pencil. Mark the rod level with gun at the start and again when it has turned 360°. Measure the distance between the marks. Be sure the jag has not unscrewed any during the process.
If it is a .222 Remington and the 14" number is right, you'll likely get best accuracy from flat base bullets in the 50-60 grain weight range. That combination likes the 53 grain flat base Sierra MatchKing especially well for maximum accuracy to 200 yards or so.
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