[El Gato]

Accuracy for a tumbling projectile is crap.

Not if it only tumbles/yaws on impact, or more properly on penetration, of the target. Which is exactly what FMJ .223/5.56x45 (and "Russian" 7.62x39 and 5.45X39) do.

[tortoise]

Not if it only tumbles/yaws on impact, or more properly on penetration, of the target.

Actually, ALL bullets tumble/yaw on impact. It isn't unique to any particular type of bullet. They are inherently unstable like that, hence the need to spin them.