I believe that "keyholes" are often the result of unstable projectiles, but quite a wide number of factors can cause that instability. Most common is the incorrect twist or an injury to the muzzle. I've seen "keyholes" at the range in guns cleaned from the muzzle.
Also a small burr on the muzzle crown could make the bullets unstable in flight.
IMHO
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"Originality can't be restored and should be at the top of any collector's priority list.
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