Misfire Troubleshooting

[Andronicus]

I was doing some shooting last night.  After shooting about 50 rounds, my Chinese SKS started misfiring each 2nd, 3rd, 4th, and 5th round (Canada, we only can have 5 rounds).  The trigger would be very hard to pull, then there would be a somewhat quieter hammer fall than usual.  Manual re-cocking would result in the round firing.  When cleaning it later last night, I made 3 observations:

1) The trigger guard appeared bent, and the trigger was making contact with it, not allowing the trigger to move to the fully forward position.  I have fixed that.

2) I found what appeared to be a mouse dropping sized piece of cleaning patch in the gas system.  I have removed that.

3) There appears to be some physical damage to the rear of the firing pin  (see picture).  I am concerned about the cause of this as I don't think there should ever be contact with this part of the pin.

I guess what I am asking is, do any of these things seem like they may be the cause of the misfires?  And What might the cause of the firing pin damage be; how can I fix it.

[Rocketvapor]

Hammer hitting the Pin with the Bolt Carrier not fully in battery. 

Could be Disconnector, Headspace, weak Recoil Spring, Pin in upside down.

Time to really examine the action.
Malfunctions like the Hammer hitting the Pin like that could be bad.

[Andronicus]

Hammer hitting the Pin with the Bolt Carrier not fully in battery. 

Could be Disconnector, Headspace, weak Recoil Spring, Pin in upside down.

Time to really examine the action.
Malfunctions like the Hammer hitting the Pin like that could be bad.

I kind of think all these problems must be related.  Could the bit of patch in the gas sytem result in the bolt not returning fully to the battery position?  How about the trigger interference?

[1mlt]

Off the bottom of my shoes I'd comment that the patch MAY have reduced the gas to the bolt causing less than full travel, resulting in a soft "hit" on the primer. I would think there would be "stove piping' with that happening though. Did you examine the primer to see if there was a "strike" to them on the misfire?

[Andronicus]

Well, I got up early today and did some shooting.  The misfire problem was reduced to 2 or 3 rounds in the total 40-is I fired.  I'll inspect the firing pin tonight.

I did notice that my gas tube doesn't sit tight against the gas port housing.  Could this contribute to a theorized incomplete cycle?

I looked at a couple of the shells that didn't fire, and the hammer mark on the primer is fairly light (much lighter than a fired primer).

Oh, and no stove-piping.

[1mlt]

Well, I got up early today and did some shooting.  The misfire problem was reduced to 2 or 3 rounds in the total 40-is I fired.  I'll inspect the firing pin tonight.

I did notice that my gas tube doesn't sit tight against the gas port housing.  Could this contribute to a theorized incomplete cycle?

YES. Put a white paper towel over the gas tube. Clock off a couple rounds and see if there i any "residue" on the paper towel? If so, leaking.

I looked at a couple of the shells that didn't fire, and the hammer mark on the primer is fairly light (much lighter than a fired primer).

Then the hammer was not moving fully forward. Something physically or lack of gas was interfering with the cycling process. Sounds like most of it was the piece of patch.

Oh, and no stove-piping.

That's a good thing.

[Andronicus]

Well, I got up early today and did some shooting.  The misfire problem was reduced to 2 or 3 rounds in the total 40-is I fired.  I'll inspect the firing pin tonight.

I did notice that my gas tube doesn't sit tight against the gas port housing.  Could this contribute to a theorized incomplete cycle?

YES. Put a white paper towel over the gas tube. Clock off a couple rounds and see if there i any "residue" on the paper towel? If so, leaking.

I looked at a couple of the shells that didn't fire, and the hammer mark on the primer is fairly light (much lighter than a fired primer).

Then the hammer was not moving fully forward. Something physically or lack of gas was interfering with the cycling process. Sounds like most of it was the piece of patch.

Oh, and no stove-piping.

That's a good thing.

Thanks for the tips.  I'm not sure when I will have a chance to do more shooting, probably next week.  I will try the white paper towel test.

What is the recommended way to force the gas tube to seal onto the port housing better?  A shim at the rear sight?

[1mlt]

Well, I got up early today and did some shooting.  The misfire problem was reduced to 2 or 3 rounds in the total 40-is I fired.  I'll inspect the firing pin tonight.

I did notice that my gas tube doesn't sit tight against the gas port housing.  Could this contribute to a theorized incomplete cycle?

YES. Put a white paper towel over the gas tube. Clock off a couple rounds and see if there i any "residue" on the paper towel? If so, leaking.

I looked at a couple of the shells that didn't fire, and the hammer mark on the primer is fairly light (much lighter than a fired primer).

Then the hammer was not moving fully forward. Something physically or lack of gas was interfering with the cycling process. Sounds like most of it was the piece of patch.

Oh, and no stove-piping.

That's a good thing.

Thanks for the tips.  I'm not sure when I will have a chance to do more shooting, probably next week.  I will try the white paper towel test.

What is the recommended way to force the gas tube to seal onto the port housing better?  A shim at the rear sight?

Something else you might try is take the firing out and be sure there isn't any 'fowling' inside the bolt. Clean it really good. Also look at the face of the bolt. Do you see any "volcano" buildup on the face?

[Andronicus]

Well, I got up early today and did some shooting.  The misfire problem was reduced to 2 or 3 rounds in the total 40-is I fired.  I'll inspect the firing pin tonight.

I did notice that my gas tube doesn't sit tight against the gas port housing.  Could this contribute to a theorized incomplete cycle?

YES. Put a white paper towel over the gas tube. Clock off a couple rounds and see if there i any "residue" on the paper towel? If so, leaking.

I looked at a couple of the shells that didn't fire, and the hammer mark on the primer is fairly light (much lighter than a fired primer).

Then the hammer was not moving fully forward. Something physically or lack of gas was interfering with the cycling process. Sounds like most of it was the piece of patch.

Oh, and no stove-piping.

That's a good thing.

Thanks for the tips.  I'm not sure when I will have a chance to do more shooting, probably next week.  I will try the white paper towel test.

What is the recommended way to force the gas tube to seal onto the port housing better?  A shim at the rear sight?

Something else you might try is take the firing out and be sure there isn't any 'fowling' inside the bolt. Clean it really good. Also look at the face of the bolt. Do you see any "volcano" buildup on the face?

I had the bolt apart last night, and gave it a thorough cleaning.  The bolt looked unfired when I bought it, and after 500 rounds, still looks quite good.

[Andronicus]

I think I may have some new useful information.  It seams that after 50 or so rounds of cheap chinese surplus ammo, there is so much buildup of powder residue (or whatever it is) on the gas piston that it doesn't move freely inside the gas tube.  Everytime I clean it it returns to free movement and seems to run problem free for 50ish shots.

The obvious solution is better ammo, but who can afford that?  Any suggestions?

[GuitarmanNick]

I usually run about 100 rounds through my Chinese SKS at each range outing. I have never had any problems with any ammunition. I have used Chinese, Yugoslavian, and Russian surplus none of which is known to be clean firing. My SKS gets quite nasty looking inside, but never fails to feed or fire.

I clean all of my firearms after firing. On my milsurps, that includes a thorough cleaning of any gas ports and related parts.

I would suggest taking a look at the gas port to be sure it is clear. I suspect it may be partially blocked which would make the accumulation of debris much worse than if it was clean.

[Andronicus]

This is becoming a recurring pattern.  I was out shooting on Saturday, and after 50 or 80 rounds, I was having the spent casings not fully extract, jamming on funny angles as the bolt closed. 

To me, and I could be wrong, this seems like an incomplete cycle.  I pulled the gas tube off to check the gas piston, but it was still moving freely.

[Boris Badinov]

Have you inspected the op rod and the extension spring?

[murray]

Does the Bolt (the one that houses the firing pin) have the serial number stamped on the left side that matches the number stamped on the left side of the receiver? Do primers look like they protrude above the back surface of the empties?

The area of your Bolt than engages the Locking Shoulder looks a little larger than normal but could just be the photo. And is that rough file markings on that surface?

[Andronicus]

Does the Bolt (the one that houses the firing pin) have the serial number stamped on the left side that matches the number stamped on the left side of the receiver? Do primers look like they protrude above the back surface of the empties?

The area of your Bolt than engages the Locking Shoulder looks a little larger than normal but could just be the photo. And is that rough file markings on that surface?

Let me try to answer your questions.
-None of my serial numbers match; the receiver and the bolt do NOT have matching serial numbers
-The primer of the casing I have with me looks quite normal.  I do not have a casing from a 'incident'.  I can look next time I am out shooting.
-As I have nothing to compare to, I can not clarify the larger than normal area of the bolt.  I can try to get a better picture posted here.
-I don't think that is rough filing markings.  I think it is low quality machining.  But I will look again with that in mind. 

Do I interpret you correctly that you think there are some significant issues with my bolt?  If so, what are the options?