I'm no expert on guns, but I would expect gun barrels to be rifled for the same reason that rifles are: Rifling makes the projectile spin as it leaves the barrel, giving gyroscopical stabilization and thus higher accuracy.
This also means that instead of flying "head first", the projectile will tend to keep its heading, even as it flies along a ballistic curve. This in turn means that in your example, the round should have LOWER penetration ability, since it is not striking the armour plate head on.
All this assuming that I haven't fundamentally misunderstood gun barrel design, ballistics, gyroscopics, or armour penetration mechanics.
And your question: is it modeled? I haven't a clue. I would guess no.