Book of the AK-47 & SKS by Patrick Sweeney

Book of the AK-47 & SKS by Patrick Sweeney.

Lots of good info on variations, modifications, ammo, etc.

Patrick Sweeney is/was a gunsmith, competition shooter and instructor in Michigan, and has written many books such as Practical Gunsmithing, The Book of the 1911, The Book of the AR (several volumes of each of those two)and the Book of the Glock.