The simplest sure way to tell the difference is to take a chamber cast, or pin gauge the neck diameter of the chamber. The 22 PPC USA case has a maximum neck diameter of 0.246", the chamber will be at least 0.2465". The Sako, if original, is almost certainly cut for this cartridge. The 22 PPC is not really standardized to the extent that the 22 PPC USA is. The neck diameter of the chamber is usually cut smaller in the 22 PPC to allow for a good fit after the 220 Russian cases have been neck turned- 0.242" or a bit less is typical.
Bob
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