SKS Gas System Mods

[nicholst55]

A couple of years ago, someone posted a thread detailing how they modified the gas cylinder on an SKS to decrease the gas pressure, and included several pix. I did have that thread saved on another computer, but... you know how that goes. It may have been Larry Gibson, I honestly can't recall.

I ran a search but didn't turn up anything on tis subject. Does anyone happen to have a link to this thread, or remember who posted it? I'd sure appreciate any assistance.

ETA: Never mind; I did some more searching and found the thread.

[Larry Gibson]

SKS GAS TUBE MODIFICATION


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 effected.

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)
Center punch
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.
NOTE:
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 SKSs have required an additional hole .3” behind the top one to subdue the ejection of of 150 gr bullet top end loads. With this tube factory 123 - 125 gr and equivalent loads ejects very softly right outside the SKS. Any reduction other than full loads (I use 22.5 gr H4227 behind the 123 - 125 gr J bullets) results in malfunctions. 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. If standard j bullet loads are going to be used with the same tube I suggest test both between each drill size.

CAUTION
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. If you do mess it up 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.

The photo shows my current 2 tubes. I have done quite a few of these for others but don't have photo's of them. The front tube is the Chinese tube and you can see the larger rear hole. It is the tube I use with my heavier 150 gr cast bullet loads. The rear tube is the original Russian tube and it is drilled for J bullet factory, milsurp and reloads. Switching out tubes is easy and it's nice to have both so you might want to consider getting a second tube also.

Larry Gibson

[JIMinPHX]

I looked at this thread a couple of weeks ago & thought that the gas tube mod was a really good idea. I was a little uncomfortable making a permanent modification though, since I'm the kind of guy that often likes to shoot downloaded ammo. Also, the idea that I might goof & go 1 size too big with the new hole made me think twice.

After pondering it a little, I came up with the idea to make an adjustable sleeve that could be moved back & forth over the new hole to tune the gun in. I drew up a few sketches while I was bored, sitting on an airplane last week. Tonight I managed to make up a prototype. It's got one goof it in that I need to fix, but other than that, it looks like a working unit.

Basically, it's made out of two aluminum blocks. The front one has a tool steel sleeve pressed into it. That one slides with about .005" of clearance. the rear block is split & clamps onto the gas tube with an Allen screw. The two blocks are connected by a pair of machine screws & pushed apart by a pair of springs. It's a pretty straight forward setup.

[MT Gianni]

Jim I like your thought process.