It is a common held belief that the Soviet assualt-rifle that went around the world in large numbers is called the AK-47 and most people call it this.
The truth is that the AK-47 was the early model and was replaced by a more basic and cheaper to manufacture model called the AKM. It is the AKM that is actually the weapon that is called the AK-47.
This may well be different in the alternative universe of Fallout 3.
You can not use spare parts from one AKM or any Soviet weapon to fix another. Such devices were rushed out of Soviet factories and the parts were made with loose precision. When a gun broke one just threw the gun away.
The repair system in Fallout 3 using other weapons to repair one would not work.
Matters may have changed now and my be different in the alternative world of Fallout 3.
Just some observations. I like the game as it is.
Well technically AKM is AK-47M, M stands for modernized. Difference between AK-47 and AKM is receiver, original is milled from solid steel, it's expensive due to material and work that is required in manufacturing. AKM's receiver is made from stamped steel sheet, that is far cheaper manufacture.
Spares taken from cannibalized weapon of same type are perfectly safe to use normally. AK's aren't any different in this respect. Certain license made AK's have some parts that could be used as spares too on Russian made AK's. If parts from original and cannibalized gun are worn it most likely would affect accuracy and reliability. AK's have earned reputation for inaccuracy, in case of Russian AK's it's due to poor quality control as parts will have quite big tolerances between them. AK was never meant to be very accurate, just accurate enough for it's job, to hit man sized target up to range of about 300m, it's sights are good enough for that. Those big tolerances are quite big part in AK's reliability in addition to basic design of weapon. 7.62 bullet would be quite deadly for lot longer ranges. Production of milled receiver AK-47's continued after AKM was adopted by Soviet army, for example Finnish army used Soviet AK's in armored units due to crews weapon racks in Soviet vehicles and firing ports of BMP's. Milled receiver is far firmer than one made from sheet and milled receiver make gun more accurate, especially if used with optical sight.
AK can be made with very high production standards, Finnish 7.62rk62 (civilian model is Valmet M62S) and 7.62rk95 (civvie version is Sako M92S) are very accurate and robust assault rifles. Drawback is cost was result of more quality control and higher grade materials. Valmet used to make stamped steel receiver 762rk62-76, but Finnish army wasn't very impressed as milled receiver is more durable and production for own army was terminated after couple production batches. M76-series was produced for US civilian market and few military customers in 7.62x39, 7.62x51 and 5.56x45.
Russian and even Chinese AK's can also be very accurate if parts are matching, those are just very rare in case of Russian guns and extremely rare in case of Chinese guns. One of my friends has Saiga M3exp, civilian version of AK-103. It's at least as accurate as most of AR-15's, he is only owner of said model of gun I know that got "positive" result of bad quality control. In general quality of AK's is very much relative production country.
FO3's gun wear out is massively over realistic level, but it adds something to game.