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It is a case-hardened bolt, but there doesn't seem to be the concern over them that there is over the receivers.

If there is a J and nothing else, the bolt is an early pre-WWI.

Usually on the top or bottom of the bolt or on the safety lug (look on all sides), about halfway up the bolt body.

What markings are on the bolt?

Does the Rock Island have a Springfield (SA) barrel from the 1927-1929 period? It appears to have a 1903A3 bolt.