5.45x39mm ammo was never made to key hole. The tip of the bullet has a air space and when it hits the steel core moves foreword into this space. This changes the center of gravity causing the bullet to become unstable. The bullet does tumble but not in a straight line. It does this in the first couple inches of penatration in soft tissue unlike other bullets that take several inches of penatration to do this. The 60grain fmj ammo imported does have the same air space in the nose of the bullet so it works the same but not having a steel core the penatration in harder targets is going to be less.
Vympel was started to mfg. 5.45 military ammo.
http://www.amursk.ru/vympel/eng_vympel.htm