Martin Foray (Updated: 8/29/2016):
The AK-47 was a revolutionary design in her own time, owing some of her success to research from the captured German wartime assault rifle - the MP43/MP44/StG44 Sturmgewehr (meaning "Storm Rifle", leading to the use of the phrasing "Assault Rifle") - generally regarded as the "Father of Assault Rifles". Interestingly, Adolf Hitler was not keen on its design at the beginning of its development and pressured for more submachine guns to go into production. As such, StG44 development by the German Armament Office continued under the guise that it was a submachine gun to cover its true battlefield nature. While the AK-47 (and the American M16 for that matter) borrowed much of the successful concepts behind the German wartime StG44, it was mechanically a Russian design. The AK-47, despite its designation (implying the service year of 1947), was actually not formally accepted into Soviet Army service until 1949. Once operational, it proved something of a departure from the wartime implements fielded by the Soviet Union during World War 2 - weapon systems that were hurriedly shuffled out of factories in less than desirable finishes utilizing cheap construction methods to meet production goals. The AK-47 sported somewhat elegant wooden furniture at points and utilized more traditional construction techniques, having her solid steel receiver machined to form. However, this certainly proved a more expensive weapon to produce in the long run especially where "mass production" and the "Soviet Army" were concerned. As such, the assault rifle series received something of a revision by the middle of the 1950s, this to become the "AKM".
The AKM - designated with the "M" to signify its "Modernized" nature - brought construction methodology back to the more economic stamped steel to help improve production speed and lower costs. The polished steel bolt was now "Parkerized", meaning that it was protected over from corrosion and resistance through the electromechanical process of phosphate conversion coating over that of the original AK-47's polished steel. The AKM was designed to accept a bayonet system that could be converted to an in-the-field wire cutter, a presumably novel concept that came into heavy use once in practice and subsequently copied by other manufacturers thereafter. The muzzle was revised to feature a lower "lip" extension to act as a simple counterweight to combat the effects of the AK-47's notorious muzzle climb and relative uncontrollability during full-automatic fire. The wooden stock was hollowed out to further reduce weight - allowing for increased two-handed precision control on the part of the operator. The bolt carrier and bolt itself - though manufactured in a slightly different style - are said to be interchangeable with that of the original AK-47 series and the chrome-lined barrel remained intact.