Greetings Finnwolf,
AR2201 had a short shelf life especially in hot conditions. It was replaced with AR2206 in the early 1980's which had improved temperature sensitivity and shelf life. AR2206 was the first powder in the series later marketed by Hodgdon as extreme powders. I would not take the risk on it. I have recently broken down some old CAC .303 rounds probably loaded with AR2201 and it was badly degraded. AR2201 was never a canister powder so varies from lot to lot.
Regards Grandpamac.
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