SKS GAS TUBE MODIFICATION
by: Larry Gibson
SKS rifles are notorious for their violent ejection of fired cases. This may be desirable on the Russian tundra at 20 below but for the reloader trying to find the brass it is intolerable. The following modification will allow the rifle to function reliably yet will deposit the brass into a small area to the right front of the shooter. It also will lessen the hazard to bystanders. Velocity of the ammunition used is not affected.
Use standard 7.62x39 ammunition or the equivalent handload with 123-125 grain bullets when making this modification. The gas system of the SKS allows for more than enough gas port pressure to drive the piston back in the gas tube and cycle the action. This was designed this way to ensure absolute reliable functioning in extreme temperatures and conditions. What this modification does is simply to “vent” the gas after it has imparted enough motion to the piston to cycle the action with out driving it so violently back. As this modification vents the gas rather quickly the use of other than standard ammunition to regulate this cycling may cause malfunctions then when standard ammunition is used.
Attention cast bullet shooters: if you want to shoot really reduced loads with light bullets then regulate it with that. With Lee's 312-155 or heavier bullets I've found functioning to be fine with the conversion made for standard ammo. When medium burning powders (4895, etc.) are used and velocity is in the 1600 fps range I've not had any malfunctions.
To accomplish this modification it will require the following tools:
15 drill bits from #45 (smallest) to #31 (largest)
Small round file
Electric drill, cordless or hand drill if power is available at range.
Before going to the range remove the gas tube from the SKS and take out the piston. On each side of the gas tube center punch .22” back from the face of the gas tube. Center punch .35” back from the face of the gas tube directly on top. Now drill each with the #45 drill. You will now have 3 holes, one on each side and one on top. The hole on top will be slightly further back from the ones on the sides. Deburr the inside of the tube with the file lightly and reassemble the piston into the tube and assemble it back onto the rifle. Load up the tools, ammo and rifle and head to the range.
Fire 5 rounds and observe the ejection pattern and how violent the action cycles. Drill out the top hole only using one size drill larger at a time. Test firing with at least 3 rounds between each drilling. You must disassemble the gas tube each time to drill.
I have found on several Russian SKSs that with 2 side holes of #45 size and the top hole of #31 size they will lay the brass into and area of about 3 feet diameter about 6-8 feet to my right front when shooting from a sitting position. The recoil of the rifle is much easier to manage as the action is not functioning nearly so violently. A couple have required the 2 side holes to be enlarged to #40 drill bit size.
Several Chinese SKSs have required an additional hole .3” behind the top one. If the first three holes have not “vented” enough gas then drill this 4th hole. Again starting with the #45 drill bit and going one size larger with a test firing each time. ( Added by res45 The numbered drill bits are wire gage bits you can get a cheap set here for about $15 that goes form #1 to #60 http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=34627
It is easy to get impatient and drill to much too quick without adequate test firing, DON’T!! You can’t put the metal back. New gas tubes are available at gun shows and out of Shotgun News for a reasonable price. If you’re not sure of your abilities get one first and try it before messing up the original. I have not messed any up using the above method. I have one tube (original Chinese tube that does fit the Russian with minimal fitting) that when used on my favorite Russian will lay the brass almost within arms reach.