Author Topic: Head space issue on SKS after polishing chamber for pitting.  (Read 2240 times)

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Pavel_J

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Head space issue on SKS after polishing chamber for pitting.
« on: October 11, 2022, 05:46:49 PM »
Recently I posted in another thread about a problem I had with a Chinese SKS I inherited that had a failure to eject problem due to a pitted chamber.

A friend had some polishing compound and told me to come by his house so we could try to polish the chamber one more time. I brought my go/nogo gauges along to check the chamber after polishing. Unfortunately it went to battery when I attempted to chamber the nogo gauge. In other words, the bolt closed on the nogo gauge.

My friend (who has a lot more experience with working on guns than me) stated that even though the rifle swallowed the nogo gauge, the rifle was still safe to test fire. He said, at worst, the rifle would only split or break a spent case. The gun would not come apart.

Since my friend lives in an unincorporated area and has a shooting lane set up on his property, we took the rifle behind his house to test fire it. The rifle passed the test and now cycles. I only put 5 rounds through it, but it appears to be functioning properly now. My friend examined the ejected cases and said there was no deformation. As far as he was concerned the rifle was good to go from now on.

I brought up that maybe the rifle needs to be checked with a field gauge to see if it would pass that. Unfortunately I don't have one, but suggested it might be prudent to buy one and not to shoot the rifle anymore until it is checked with the field gauge. My buddy seemed offended that I didn't agree with him, but said it was my money to waste if I wanted to buy a field gauge or pay a gunsmith to do it. He said I was worrying about nothing. He gave a list of reasons why it isn't unsafe to continue using a rifle that has failed a nogo check.

What would you do? What is your opinion about what I described?


Rocketvapor

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Re: Head space issue on SKS after polishing chamber for pitting.
« Reply #1 on: October 11, 2022, 06:56:38 PM »
A field gage would be the answer.
There is a way to measure headspace past a go/no go with shims. 
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Filroy77

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Re: Head space issue on SKS after polishing chamber for pitting.
« Reply #2 on: October 12, 2022, 01:09:27 AM »
Recently I posted in another thread about a problem I had with a Chinese SKS I inherited that had a failure to eject problem due to a pitted chamber.

A friend had some polishing compound and told me to come by his house so we could try to polish the chamber one more time. I brought my go/nogo gauges along to check the chamber after polishing. Unfortunately it went to battery when I attempted to chamber the nogo gauge. In other words, the bolt closed on the nogo gauge.

My friend (who has a lot more experience with working on guns than me) stated that even though the rifle swallowed the nogo gauge, the rifle was still safe to test fire. He said, at worst, the rifle would only split or break a spent case. The gun would not come apart.

Since my friend lives in an unincorporated area and has a shooting lane set up on his property, we took the rifle behind his house to test fire it. The rifle passed the test and now cycles. I only put 5 rounds through it, but it appears to be functioning properly now. My friend examined the ejected cases and said there was no deformation. As far as he was concerned the rifle was good to go from now on.

I brought up that maybe the rifle needs to be checked with a field gauge to see if it would pass that. Unfortunately I don't have one, but suggested it might be prudent to buy one and not to shoot the rifle anymore until it is checked with the field gauge. My buddy seemed offended that I didn't agree with him, but said it was my money to waste if I wanted to buy a field gauge or pay a gunsmith to do it. He said I was worrying about nothing. He gave a list of reasons why it isn't unsafe to continue using a rifle that has failed a nogo check.

What would you do? What is your opinion about what I described?

Here’s a thread that’s leading to what you are looking for. I say that cuz I only read the first page.

I used the shim method on a old .30 carbine. It works. I found that the head spacing was a good bit over the allowable limit. There is a number for the SKS but I don’t know what it is.

 The primers were backing out of the cases on that particular weapon.

http://www.sksboards.com/smf/index.php?topic=48053.0

Another:

https://www.google.com/search?q=headspace+www.sksboards.com%2Fsmf%2Findex.php&ie=UTF-8&oe=UTF-8&hl=en-us&client=safari
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xtriggerman

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Re: Head space issue on SKS after polishing chamber for pitting.
« Reply #3 on: October 12, 2022, 12:52:09 PM »
  Like I said in Filroy's link, tilting bolt actions are the easiest actions to test head space than any action on earth Without a headspace gauge. Perfect headspace on any firearm is about  .004-.007 worth of space between the in battery bolt face and face of a chambered factory cartridge. In the SKS, put the stripped bolt in battery against a factory cartridge and feeler gauge the gap between the bolt and locking shoulder. If your gun did not pass the no go gauge test, I'm guessing you have more than 8 or 9 thousandths there on feeler gauges. You could be only 2 thousandths more than a no go gauge would allow and be perfectly OK shooting the gun. The gauges are great for chambering a brand new barrel but in practicality, they are not the last word in safety. That, must be calculated as to a specific amount of headspace in the gun and cartridge being used. For instance, Black powder cartridges work on so little pressure, head space is like hand grenades, "close enough" is good enough. So a few factors can be put in place as to if a gun that fails a no go test is safe enough to fire. First is by how much space, Cartridge pressure ratings and cartridge casing design. And in the end, if the test failure is by an insignificant amount such as .004-.006 over and beyond the .007 max, a close inspection of fired cartridges will tell you alot about and approaching unsafe stress in the firing process. On this particular cartridge, you can take into account the cartridge design is pure military in that the casing features alot of strength in the head end of the cartridge, So it can handle bad head space bulging well and would more likely just split at the neck in a unsafe head space condition as well as bowing out primers or just ejecting cartridges with raised primers. Bore condition also plays into the issue. So to sum it up, feeler gauge your locking shoulder space, that will give you a hell of alot more info on the safety of your gun than a no go gauge. You can even do the test with the No Go gauge chambered up for exactly why the gauge is insufficient by exactly how much. No need to guess anything here with a tilting bolt gun.
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murray

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Re: Head space issue on SKS after polishing chamber for pitting.
« Reply #4 on: October 20, 2022, 10:37:55 AM »
I use scotch tape on my No-Go gauge, trimmed with a razor blade to fit the round head. The tape is approximately .002" thick and if you only over by .001" then you'll feel the Carrier lock up before going fully into battery. Then add another layer of tape if it does close on 1 layer, .004" over?...safe but not the most accurate maybe, and if need be, add a third layer of tape, and if it doesn't lock up before closing, do all the things mentioned previously. Find a field gauge...watch primers on empties...etc

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Pavel_J

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Re: Head space issue on SKS after polishing chamber for pitting.
« Reply #5 on: November 26, 2022, 08:33:53 PM »
Find a field gauge...watch primers on empties...etc

This is an update to this thread I started back on October 11. Since polishing the pitted chamber to the point that the rifle finally started functioning reliably, I have shot over 200 rounds through it without any malfunctions. I also got the rifle sighted in as close to zero as I could with my 66 years old eyes using iron sights. The pitted rifle was about on par with the other two SKS rifles I own at 50 and 100 yard groups.

After each shooting session I gathered up the spent cases to examine them for problems and found none. No bowed out or raised primers. No split or bulged cases. On the brass cases I can see some faint impressions of the remaining pits in the malleable brass, but the spent cases ejected flawlessly. The spent steel cased ammo looked good and eject flawlessly. All the spent cases look just like the spent cases from the other two SKS rifles I own.

I was gaining confidence in the safety and reliability of the rifle after running over 200 rounds through it, but there was a gnawing in the back of my mind that I just had to know for sure how safe the rifle really is after polishing out an unknown amount of metal attempting to fix the corroded chamber pitting. After the last and final polish job, I will admit sometimes I was getting minor blowby of gasses and debris that I don't get while shooting my other two SKS rifles. This worried me. Since I have four other rifles that also shoot 7.62x39, I decided to buy a 7.62x39 CIP Field Gauge from Toth Tool & Engineering and it arrived in the mail this afternoon.

To my disappointment, the rifle in question swallowed the Field Gauge. The bolt went to battery easily. Reluctantly I decided to take the rifle out of service. After all the work I have put into the rifle since inheriting it from my deceased friend's estate, I have come to the conclusion that is the prudent course of action. Of course there are other folks that would do otherwise and continue to use the rifle. That is their choice. I have many other guns in my collection and see no reason to go there. I probably shouldn't have put 200+ rounds through the rifle before buying a Field Gauge, but that is hindsight. I know better now. Ignorance is bliss. I did what I did up to now and fortunately nothing bad happened.

On another note, since I have two other milsurp SKS rifles (one Chinese & one Russian), I decided to see what my newly acquired Field Gauge would do in them. Both passed with flying colors and failed to go to battery using the Field Gauge. Hurray! That is good information to know and well worth the price of the Field Gauge (in my opinion). The last two rifles I own in that caliber are factory new and I was too lazy to test them today, but will eventually get around to it. I would be extremely shocked if they fail since they are brand new and not milsurp. 

In case anyone is wondering about my future plans for the rifle. I'll keep it around for spare parts. I definitely would not sell it to an unwitting buyer knowing what I know.

Filroy77

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Re: Head space issue on SKS after polishing chamber for pitting.
« Reply #6 on: November 26, 2022, 09:59:00 PM »
It’s a bummer when you discover a weapon has outlived its usefulness. At the very least I would remove the firing pin just in case. Personally I would strip the weapon of all useable parts and destroy it. That’s what I did with the .30 Carbine that was just flat worn out. I think every recruit that came down the pike trained with that rifle. LOL
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LESchwartz

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Re: Head space issue on SKS after polishing chamber for pitting.
« Reply #7 on: November 27, 2022, 10:46:41 AM »
I don't know how easy it might be to fit a replacement barrel.  However, I would probably remove the firing pin until you get it sorted.

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Pavel_J

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Re: Head space issue on SKS after polishing chamber for pitting.
« Reply #8 on: November 27, 2022, 07:40:42 PM »
I don't know how easy it might be to fit a replacement barrel.  However, I would probably remove the firing pin until you get it sorted.

Larry
For this particular rifle I don't believe it would be economically practical to replace the barrel. The money it would take to do that would be better spent buying another rifle. If the head space would have been within specs after polishing out the pits causing the ejection issues, it would have been practical. The original ejection problem was fixed with a series of polishing jobs on the chamber, but the cure killed the patient. It ejects beautifully now, but the head space is no good.

If there was an economical way to fix the head space problem using the parts already on the rifle I would be open to that. On the pinned barrel AK platform I have read it is possible to set back the barrel to correct head space issues using oversized pins, but my rifle has a long lug screwed barrel and is an SKS. An entirely different animal. A lot more complicated and more expensive than just changing pins from what I have read.

My inherited Chinese Norinco rifle manufactured in 1959 or 60 at Factory 26 has no collector value because only the receiver and magazine have matching numbers. All the other components are a hodge podge of non-matching parts put together by the US distributor that imported it from Norinco during the pre-ban days. The distributor was a company named Davidson's. These guns were selling for $70-$80 back then at Texas gun shows along with plenty of cheap Chinese milsurp corrosive ammo.  These guns are pretty on the outside, but quickly turn rotten on the inside if you don't clean them after using the cheap corrosive ammo. That is what my buddy did and I ended up with the gun after he died. He shot the gun and never cleaned it from what I discovered after I got it..

I will remove the firing pin and tag the rifle as unsafe to use--parts gun only.