SK-17 (Semiautomatic Kalashnikov 2017) is a custom AKM-based rifle built by a company called Fire Control Group Manufacturing. Besides being a custom made rifle, it has several design changes which are supposed to increase the efficiency of the rifle.
The first difference from the AKM is that the gas system has been shortened by drilling the gas port closer to the breech. According to the company officials, this allows to increase the rigidity of the barrel and reduce the leverage of forces acting on the barrel during firing. The gas piston has also been shortened to fit the shorter system.
The second difference is the heavy barrel contour. The thicker barrel profile should allow higher resistance to heat which is important for intensive firing. Of course, the cost of the heavier barrel profile will be the weight increase.
Last but not least, the third design change is the use of proprietary twist rate and rifling type which results in muzzle velocity increase. The manufacturer claims 100-200 fps of muzzle velocity increase with standard 7.62x39mm ammunition compared to conventional AK rifles with same barrel length. My initial thoughts after hearing this statement were that the MV increase must be achieved by pressure increase, which would mean a use of a stronger bolt and front trunnion. I contacted the manufacturer to find out if that is the case and here is what they told me:
The design allows for optimal powder burn and as far as we can tell the chamber pressures are no higher than a standard barrel. In fact, I believe them to be lower, based upon lack of overpressure sign on the spent casings when compared to our control barrels casings, the SK-17 seems to be easier on brass than what we typically see from AKs. We use a standard AKM bolt and trunnion that we just do a little work on the mating surfaces between the bolt and the trunnion.
The 16.3″ barrels are made of 4150 CMV steel and feature chrome lined bores. The muzzle of the SK-17 rifle is threaded with 14x1L left-hand metric thread pitch which is the standard AKM thread pitch. The company also points out that their barrels have a correct groove diameter of .311″ for the 7.62x39mm cartridge. The Soviet/Russian .30 caliber firearms (7.62x39mm, 7.62x25mm, 7.62x54mmR) have the standard bore diameter of .300″ (land to land), but they traditionally have deeper grooves than the US standard which results in slightly larger diameter bullets (7.92mm (.3118″)).
As expected from a custom rifle, the SK-17 has hand fitted parts and smoothened action. The finish on this rifle is Cerakote over the manganese phosphate. The rifle also comes with a Magpul MOE pistol grip, Magpul ACS stock, Midwest Industries Gen2 M-LOK handguard, ALG AKT trigger, Saberwerks 13 KOP scope mount, JMac Customs GBC-13 front sight/gas block combo, JMac Customs RRD-4C Slim muzzle brake and FCGM MDDB (muzzle device detent block).
Many thanks to William Rich and Tommy Kirk for the provided information.