HikingVetUp the barrel of a Decommissioned gun.
That's very interesting; it seems to have a progressive twist rate. I assume that this is from a large bore armament of some kind? I believe that gain twist is sometimes (usually?) used on artillery. (See: https://www.youtube.com/watch?v=KI-_CtmOzFs)
Ask Ian: Progressive Twist (Gain Twist) in Small Arms?
Rifiling can’t have too tight of a twist or it will cause overheating, jams, and other negative effects on the rounds. The same twist is (at slightly different profiles) used on most modern firearms and artillery.