Before you even get started on the adjustment, the gas system and the chamber have to be spotless.
The SVT has a fluted chamber neck to compress the case neck and aid in extraction. If it's not clean, the bolt will rip the case in half, and eventually break the extractor. Parts for these rifles are not easy to find.
The gas adjustment nut is held in place by the gas piston. The gas cylinder covers the piston and drives the bolt actuating rod back.
Corrosive ammo that was used in these guns causes havoc on these two critical parts. Piston and cylinder need to be cleaned after every use. They also need to be within specs. I have a source for these parts made in stainless steel if you need them. New made recoil springs too.
4 tools you'll need are a SVT gas adjustment wrench, a rubber mallet, a SKS sight adjuster, and a broken case extractor will keep your day from being ruined. The SKS tool works on the SVT sight, and will double as a stock crossbolt tool as well. On a side note, the SVT was designed to be loaded with Mosin stripper clips with the magazine in place.
The gas adjustment nut has 5 flats with numbers stamped on them. The flat facing straight up, and lined up with the index mark, is the setting the rifle is shooting at.
For any given ammo, start at the lowest setting of 1.1. If the bolt doesn't cycle and eject the spent case, set the butt of the rifle on the ground and use the rubber mallet on the bolt handle to eject it. Turn the setting up to the next flat, making sure it's lined up perfectly. It has holes that have to be lined up with the gas port in the muzzle extension and barrel.
Repeat this procedure until the case ejects about 5 feet from you. Any more than that, and you risk damage to the rifle.
Light ball works the best, brass cases feed the best. Copper washed cases may have some feeding issues with reproduction mags. Lacquer coated cases work well if you keep the rifle from over heating with rapid fire, and they get hot fast! The lacquer melts off the case and gums up the chamber and flutes. A bronze .45cal bore brush and carburetor cleaner from the breech end will clean the chamber out and give positive extraction.
This gas adjustment tool fits better than an original, and a fraction of the price. http://www.blackrivergunsmithing.com
I noticed what appears to be a pin or something below it. Is this part of the adjustment? Is it a locking pin or something? If so, how is it suppose to move?
That's the muzzle extension wedge that holds the muzzle extension to the barrel. Don't remove it unless absolutely necessary!