Moved your post to the ammo/reloading board as it will get more visibility here and your question has to do more with the ammo than the gun.
One thing I would recommend doing just to rule it out is do a chamber cast to make sure there's nothing screwy with the barrel itself. Bore scoping the barrel would also be a good idea just to make sure there isn't some flaw in it that's causing the pressure spike.
Beyond that, I would try a more seasoned and proven powder for the .300 Savage like H4895 or RE-15 just to see if the problem persists with a different powder.
Some good load info here:
https://www.24hourcampfire.com/ubbth...0_Savage_Loads
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