I think currently all the major powers have smooth bore main armament in many of their tanks ( or are coming in to service) with finned projectiles.
Obviously a finned projectile will absorb a great deal of energy from the fin drag as it spins decreasing velocity and range. A very slow spin can still help stabilize finned projectiles and the current smooth-bore projectiles have the fins very slightly off-set to create a slow spin.
To get no spin or slow spin with finned projectiles with traditional grooved barrels they have "Obdurating Rings" which is a collar that seals the gas but slips on the projectile. There are also various discarding sabot designs that seal the gas but fall off once the projectile leaves the barrel. These are extremely bad news if infantry have close support from tanks firing over their heads!
I believe Mike's projectile would have been shot from a smooth-bore weapon but may be wrong.
Lang
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