All bullets will tumble when entering the human body, although all at different rates, even different types of 7.62mm or 5.56 mm ammo will differ.
To simplify, a round which hits a body will generally do one of three things:
1. go straight through. This is called a through and through wound and usually causes the least damage, depending on where it hits;
2. tumble. This causes more damage; or
3. shatter. This usually causes the most damage.
Generally a softer bullet is more likely to shatter, but it generally does not carry as far and may have trouble penetrating protective clothing, so there is always a compromise involved.
Incidentally, that is the theory behind the "double-tap", namely if you fire two bullets, the odds are very high that at least one will tumble and cause a serious wound.
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