It's no secret, I'm a fan of the AK rifle. There are several reasons for my interest in the AK rifle, but I can sum up that interest by describing the rifle as "stupid simple". A fighting rifle needs to be simple. Simple controls. Simple sights. Big parts that facilitate easy maintenance, and it needs to be reliable. The AK is the epitome of simplicity and reliability. That's why I prefer the AK, it's a no frills tool designed to be brutally effective, which it is.
Here in the U.S. we're in love with our AR15's and M16's. I'm also a fan of the AR15 and M16, but stupid simple it is not. It has tiny parts that are easily lost in the field, things like the firing pin retaining pin. It gets dirty more quickly than other rifles that don't rely on direct impingement to operate the action. But if kept clean and the troops are properly trained, it's a world class military small arm. But the feature that has set the AR15/M16 apart from the AK in the last couple of decades is the ability of the AR15/M16 to mount a dizzying array of aftermarket accessories. Some are more useful than others, but accessories such as modern optical sighting systems are critical updates for a modern fighting rifle.
The countries that field the AK have developed sighting systems for the rifle, but in my opinion most of these systems are far behind Western technologies in terms of quality, durability, and usefulness. As an example, the Russian Kobra red dot sight is a popular optic used on AK's. It mounts to the rifle via a proprietary rail system that resides on the left side of the AK's receiver. The red dot sight (RDS) sits high above the rifle thereby not allowing a co-witness of the iron sights. In my experience the Kobra sights are somewhat frail as well. They certainly aren't in the same league as the Aimpoint Comp M4, as an example.
As the popularity of the AK grows in the United States, more companies have focused on developing high quality, well engineered solutions for mounting modern sighting systems to the rifle. A number of things have driven the popularity of the AK in recent times, but mostly the relatively low cost of both the rifles and ammunition have been the primary contributors to this popularity. Whatever the reason, it's a definite win for those of us who own AK's as we're now seeing some great accessories that rival those offered on the AR15/M16.
One of the more useful developments for the AR15/M16 have been the forward mounted rail systems used to mount various accessories. Until recently, these weren't available for the AK rifle. One of the pioneers was the Ultimak rail for the AK, but it left much to be desired. It replaced the gas tube with one that included a 1913 style rail for mounting optics. The downside is that the gas tube gets extremely hot during extended firing and it then passes this heat along to the optic mounted to the rail. You also had to cut up the lower hand guard or remove the heat shield to get it to mount properly. But companies like Midwest Industries came along with a more integrated solution that not only runs cooler but allows you to mount modern RDS systems low enough to allow a co-witness of the iron sights.
The AR15/M16 also evolved to include a flat top 1913 rail along the receiver that compliment after market railed hand guards. This allowed the user to mount more traditional optics like scopes closer to the shooter for proper eye relief. While the Russians did develop scopes based on the receiver rail mounting system, these are of modest quality and set off center, to the left, making it difficult for left handed shooters. This system has mostly been unpalatable to many Western shooters. That left the door open for Texas Weapon Systems to develop a reliable method for mounting a 1913 rail to the receiver of the AK, which they did. This system allows the shooter to mount conventional optics in the proper location while not interfering with the normal operation of the AK, including the ability to easily field strip it for cleaning.
Source : Military Arms Channel Blog: Modernizing the AK