The Starter MBR
Most militiamen will not initially have the funds to provide themselves with top of the line gear and many turn to the SKS as the 'good enough' MBR. The problem begins when owners try to turn the SKS into a Dragunov sniper rifle or an AK-47. In the end, the conversion will have cost more than simply purchasing the desired firearm and the SKS will not preform nearly as well. The first lesson of the SKS is that it is best left as it was designed and for the militiaman to adopt tactics that compliment the SKS.
Current Market Value
A SKS will run from $150 for a well worn Yugoslavian (Yugo) to well over $500 for good condition Russian or Chinese 'Paratrooper'. The average going price is $200 to $250 for the more abundant stock Yugoslavian model.
The SKS is a Soviet 7.62x39mm caliber semi-automatic carbine, designed in 1945 by Sergei Gavrilovich Simonov. SKS is an acronym for Samozaryadniy Karabin sistemi Simonova (Russian: Самозарядный карабин системы Симонова), 1945 (Self-loading Carbine, Simonov's system, 1945), or SKS 45. The Soviets rather quickly phased the SKS carbine out of first-line service, replacing it with the AK-47, but it remained in second-line service for decades afterwards. It remains a ceremonial arm today. It was widely exported and produced by the former Eastern Bloc nations, as well as China, where it was designated the "Type 56", East Germany as the "Karabiner S" and in North Korea as the "Type 63". It is today popular on the civilian surplus market in many countries. The SKS was one of the first weapons chambered for the 7.62x39mm M43 round later used in the AK-47 and RPK.
A standard SKS is semi-automatic and has a fixed/hinged 10 round magazine which is loaded from the top of the rifle either by manually inserting the ammunition one round at a time or with a 10-round stripper clip. In typical military use the stripper clips are disposable. If necessary they can be reloaded multiple times and reused. The SKS is a gas-operated weapon that has a spring-loaded operating rod and a gas piston rod that work the action via gas pressure pushing against them. Also, it has a "tilting bolt" action locking system. Some variants of the SKS have been modified, with limited success, to accept AK-47 detachable magazines (military rifles designed with fixed magazines often experience feed jams when modified to accept detachable magazines, and the SKS is no exception). Norinco had, at one point, manufactured the SKS-M, SKS-D, and MC-5D models which were engineered from the factory to accept AKM magazines without problems (though the wood stock must be relieved to accept drum magazines). The SKS also has a slightly longer barrel than AK-series rifles, with a fractionally higher muzzle velocity.
While early Russian models had spring-loaded firing pins, most variants of the SKS have a free floating firing pin within the bolt. Because of this design, care must be taken during cleaning (especially after long storage) to ensure that the firing pin does not stick in the forward position within the bolt. SKS firing pins that are stuck in the forward position have been known to cause accidental "slamfires" (uncontrolled automatic fire that empties the magazine, starting when the bolt is released). This behavior is less likely with the hard primer military-spec ammo for which the SKS was designed, but as with any rifle the user should properly maintain their firearm. For collectors, slamfires are more likely when the bolt still has remnants of cosmoline embedded in it. The firing pin is triangular in cross section, and slamfires can also result if the firing pin is inserted upside down. Third party kits are available that can put old-style spring-loaded firing pins in SKS's that did not come with them, increasing the reliability and reducing the chance of slamfires.
In most variants (Yugoslav models being the most notable exception), the barrel is chrome-lined for increased wear and heat tolerance from sustained fire and to resist corrosion from chlorate primed corrosive ammunition, as well as to facilitate cleaning. Chrome bore lining is common in military rifles. Although it can diminish practical accuracy, this is not a real limit on field grade accuracy in a weapon of this type.
All military SKSs have a bayonet attached to the underside of the barrel, which is extended and retracted via a spring-loaded hinge (some are removable whereas some are permanent). The SKS is easily field stripped and reassembled with no tools. The rifle has a cleaning kit stored in a trapdoor in the buttstock, with a cleaning rod running under the barrel, in the same style as the AK-47. In common with some other Soviet-era designs, the SKS trades some accuracy for ruggedness, reliability, ease of maintenance, ease of use, and low manufacturing cost. The SKS is a simple design that is highly effective and rugged.
There are many after market accessories for the SKS that could add many hundreds of dollars to the final cost of a SKS build. In my opinion only one is necessary, the rest are only a means to turn the SKS into something it is not and never will be: an AK47 type MBR. The following list is in order of importance.
Firing Pin Upgrade: This is the must have upgrade for the SKS. Spring loaded firing pins can be obtained from http://www.murraysguns.com for $40(+-)
Trigger Upgrade: Wolff Gun Springs makes a set of replacement springs
that will reduce the overall trigger pull.
There can also be an issue with the sear in which bumping the rifle can cause it to fire. For more info check out:
Peep Sight Upgrade: Since some prefer the AR type peep sight over the SKS leaf sight, there are two options: Mojo MicroClick which replaces the leaf sight and TechSights which mounts on the rear of the receiver cover.
Muzzle Upgrades: Not needed, but you best option is to have the barrel threaded by a gun smith. If you feel you just have to have a flash hider\ muzzle break then get a pin-on version that uses the FSB pin slot.
Box Magazine Upgrade: Just don't do it. Use the stripper clips and be happy with ten rounds in the provided box magazine. But if you insist on using the duck bill magazines then please stick with the Tapco 20 round polymer mags. They have the best reputation and are reasonably priced. Warning you are now in 922(r) territory.
Stock Upgrade: Again, just don't do it. But if you insist try the Ramline sporter stock or the Tapco T6. And again, you are now in 922(r) territory.
Scope Upgrade: The worst upgrade of all. The SKS does not have a reliable mount point for a scope in its stock configuration. The best option is to drill and tap the receiver and use an AK style mount. Next is the ScoutScope system (http://www.scoutscopes.com/) which replaces the rear sight. Finally are the receiver and gas tube mounts, both of which provide an inconsistent remount point at best and a moving mount point at its worst.
The bottom line is that these 'upgrades' will cost you in the long run and you would have been better off buying and AK or a Saiga from the outset.
Survivor's SKS Board - The #1 SKS resource on the Web
Surplus Rifle - Another good resource for How-Tos
Tapco USA - The home top shelf SKS furniture and parts.
Tech Sights - SKS Peep Sights
Mojo Sighting Systems - The other peep sight maker.