Wow... in my opinion there is a ton of hyperbole in the above replies.
I think the ak74 is a fantastic option if your looking for a trail gun. I would assume this might be for a truck or while working in a ranch scenario. The 5.45x39 is slightly ballistically inferior to the 5.56x45 of the AR platform, but it seems to be the superior design. The bullet itself is built with a small air pocket directly behind the nose. This air pocket, created by accident by the way, forces the bullet to yaw and turn within 3" if impact into a mass. AK74 rounds have been know to turn almost 90 degrees within target media, and penetrates the same 12" of the 5.56x45 round. While the typical 5.56x45rd need a 18"+ barrel to give the required velocities needed for the round to fragment and tumble, the smaller russian round reliably tunbles all the time, but it does not fragment. I see it was a wash. Fragmentation gives a little extra damage to the temp cavity, but the Russian round create a larger more damaging cavity. Apples and oranges.
It seems that the Russians stumbled upon the correct formula of power, size, mass and design when they attempted to reverse engineer our 5.56x45 round. They copied some succesful Yugo experiments they did with the 7.62x39 and air pockets in the tip. The round produces almost no recoil in the AK74s, is fascinatlingly cheap right now and deadly.
It's flat shooting, has a very high velocity, and very minimal recoil, especially when used with the AK-74 muzzle brake. The Russians essentially found a way to "cheat" the Hague Conventions which regulate military ammunition. The Hague Accords ban the use of hollow point, exposed lead, or other type of bullets that are designed to expand and cause maiming of humans. Because of the Hague Accords, military bullets are full metal jacketed and specifically built NOT to expand. The Russians took the idea of a small caliber bullet that was very stable and accurate in flight, but that destabilized once it hit, and tumbled, causing greater wounding. They developed the 5.45x39 round which was specifically made to tumble wildly on impact. The bullet has a mild steel outer jacket with a copper plated coating to prevent rust and to lubricate the bullet during feeding. Inside the outer jacket is a slightly harder steel core, which is NOT an armor piercing core, even though it's reported to be able to penetrate both sides of a US steel helmet at 300 meters and author David Fortier was able to put a 5.45x39 through both sides of a US Kevlar helmet at 300 yards. This mild steel core is flat on the ends and slightly tapered on both ends. On top of the steel core and surrounding it on the sides, is a soft lead cap. In the tip of the bullet is a hollow air space. This produces a bullet that's weighted toward the rear, and makes it very stable in flight, but which causes it to destabilize once it hits.
While the 5.45x39 is not as accurate or powerful as the US .223/5.56x45, it does appear that the Russians have succeeded in fielding a bullet that out performs the US bullet. The Russian military including Spetznaz prefer the 5.45x39 and consider it the best rifle and round in the world.
Here's a sectioned 52 grain 5.45x39 7N6 PS bullet.
Note the mild steel outer jacket, the slightly harder tapered and flat ended steel core, the lead cap on top and around the core, and the hollow air space.
I researched this round alot and am sold on it and the platform as a good all-around LIGHT performer. If I am looking for a carbine, this would be it. It is not a MBR round, and I would not take it over a 7.62x51 or one of the slightly lighter 6.* offerings. But then again... for $600 you get a combat ready carbine and 2K rounds to practice with and use. Great deals.
I got the image from a similar post on the TFL a little while back.
