The majority of these documents describe and illustrate improvised modifications that can be performed in any fairly well equipped home workshop.
Firearm modification is done in order to enhance performance or to facilitate hiding the weapon. Firearm modification can include anything from a trigger job to putting in a bull barrel to polishing up internal parts to make it run smoother.
Two of the most modified guns are the Ruger 10/22 and the AR-15. There are many, many different companies that manufacture after-market stocks, barrels, triggers, sights, and internal parts for these guns. There are companies that also make kits to convert a centerfire pistol to shoot rimfire .22LR, as .22 cartridges are far cheaper to practice on.
This concise instruction manual explains, with the use of diagrams, how to convert an SKS carbine to accept Ak–47 mags.
Details the modification of magazine, trigger, bolt, frame, new magazine catch, and stock.