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Discussion Starter #1
So I recently bought a Norinco SKS. It's a good gun and shoots well.

So I'm doing a full strip-down of it, and when I take off the gas tube I had the rifle in my lap, pointed slightly downward...

The gas piston fell out and struck my kitchen floor. When I was putting the rifle back together I couldn't get the front head of the gas piston to enter the gas tube. Striking my tile floor put a small dent in the head of the gas piston, and it didn't have clearance in the gas tube.

Enter my dremel tool, and I grind off the minute deformed protrusion, and I get the gas piston to seat and travel in the gas tube. But it seems as though it might not be traveling as far back as it should.

So the gas tube's front 1/3 is an exposed metal tube, and the back 2/3 is covered with a wooden handguard. About 2/3 of the way back on the exposed metal portion there are two small holes in the gas tube. I'm assuming these are for gas bleed-off after the head of the gas piston has traveled backwards beyond these holes.

My piston head only travels backward about 1/2 the length of the exposed metal portion, and never gets to, nor clears, these holes.

How far does the gas piston move backward on a properly functioning SKS gas tube?
 

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Discussion Starter #2
Actually, I just found my own answer. My google fu was just a bit slow this evening...

http://www.sksboards.com/smf/index.php?topic=18494.0;wap2

3. I would like to know how far the rod is supposed to travel into the chamber when it cycles against the bolt.
5/8" maximum throw. The gas system should be able to move it the full distance but a weak system won't be able to overpower the op rod spring plus the bolt carrier spring. Quote

4. How far does the gas piston travel back into the gas tube, i.e., how much of the small end of the piston sticks out of the receiver side of the gas tube if you hold it up and let it slide all the way down? Does the piston head travel past the two little holes in the gas tube or not?
The gas piston and op rod both travel identical distances. If you look at the way the system works, if the bolt is in battery you will see that there is a solid line of steel from the valve itself, which is in contact with the gas piston, which touches the "op rod" (AKA piston extension), which touches the bolt. (There might be a thousandths of an inch of gap between any of those pieces but ideally they are touching so there is an incredibly smooth transfer of energy from the barrel to the bolt.) Like Billy said, those little holes are to eliminate the backpressure that would be caused by piston movement.
 
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