My $.02:
If you take the shape into account, it would be difficult for the ID to decrease as the material would have to expand into itself...so to speak. Expansion would come from the heated molecules' increased movement. There would be less resistance outward and therefore the direction of expansion.
As far as velocity increasing...does the heat increase in the barrel due to friction affect the powder in the cartridge? Would the increased heat cause the powder to burn faster and propel the bullet at faster velocity?
If you take the shape into account, it would be difficult for the ID to decrease as the material would have to expand into itself...so to speak. Expansion would come from the heated molecules' increased movement. There would be less resistance outward and therefore the direction of expansion.
As far as velocity increasing...does the heat increase in the barrel due to friction affect the powder in the cartridge? Would the increased heat cause the powder to burn faster and propel the bullet at faster velocity?