How to Remove a Mossberg 500 Stock (4 Steps)

Check that the shotgun is unloaded by placing the safety and the 'on' position, pressing in the slide release (located next to the trigger housing), and opening the action by pulling back on the fore-grip.
Use a standard size Philips head screwdriver to remove the screws holding the butt-plate (the rubber pad on the end of the stock) in position and remove the butt-plate.
Look down the exposed hole on the rear of the stock and determine the bolt head configuration (some Mossberg models have a slotted head and some utilize a 1/2-inch hex head).
Use your standard screwdriver or your Allen wrench (depending on which configuration you found) and remove the bolt by rotating it counter-clockwise. The stock will now come off the receiver.

How to Remove an SKS Stock (10 Steps)

Flip the switch on the right side of the rifle to a vertical position and pull the pin outward.
Remove the receiver cover and buffer assembly by gently pulling backward.
Pull the charging handle back to remove both the bolt assembly and the charging handle.
Turn the rifle upside down and set it on a smooth surface.
Use a Phillips screwdriver to press down the button behind the trigger loop. This will cause the trigger assembly to pop up. Be careful: The trigger assembly is spring-loaded.
Turn the rifle over and lift the barrel assembly out of the stock.
Flip the lever in front of the rear-sight post to release the gas tube assembly.
Remove the gas piston.
Using a small nail or hole punch, push the retaining pin out of the back of the rear metal cover of the handguard.
Remove the wooden handguard. You can now attach the new stock.