At what distance were you getting keyholes ?
What sort of velocities were you working with?
It is possible that the bullet had not had time to stabilize yet.
It may have been unstable at 100yds but was stable at 200 yards.
Next thing to check would be the crown.
I would verify the twist rate of the barrel.
Also being it is a longer bullet it takes more spin to stabilize....the physically longer the bullet the faster twist barrel you need. 1:7 may not have enough twist until you get to higher velocities. Being you mentioned some keyholes, I suspect that may go away with higher velocity as you may be on the edge of stability.
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