The Afghans called the 5.45 "the poison bullet" or "the devil's bullet" for the bad wounds it caused.
It causes increased wounding because the bullet was specifically designed to tumble inside the body, tearing tissue and organs, and bursting bones.
When the Soviet's decided to design their answer to our 5.56 round, they specified that the new round had to be no less effective then their standard 7.62x39.
They decided that the way to make that happen was to design a bullet that would tumble rapidly in the body.
This was basically a means of cheating on the Hague Conventions on the use of expanding bullets which caused maiming wounds.
The Soviets could claim the 5.45 wasn't covered by Hague because it was a full metal jacket, non-expanding bullet.
The 5.45 works by moving the center of gravity to the rear of the bullet. This makes the bullet more stable in flight, and therefore more accurate.
However, once the bullet hits, it destabilizes very quickly and tumbles sooner and faster than the 7.62x39.
The 7.62x39 starts to tumble after penetrating about 7 3/4" and usually tumbles once.
The 5.45 starts to tumble in 2 1/2" and tumbles at least twice.
If the bullet stays in the body, near the end of travel it makes an almost 90 degree turn off the path of travel. This "hook" in an odd direction makes finding the bullet difficult without an x-ray, which isn't available on the battle field for most countries.
The effectiveness of the 5.45x39 is certainly.y not an issue with the Russians and especially the Russian Spetznaz, who use it in preference over the 7.62x39. The 5.45 built an impressive reputation in Afghanistan, Chechnya, and Georgia.
Nothing succeeds like success.
Here's a sectioned 5.45x39 7N6-PS bullet.
Note the copper plated mild steel outer jacket, the blunt mild steel inner core, the lead "cap" on top of the core and surrounding it between the core and outer jacket, and the hollow air cavity in the nose:
