Barrel/Receiver Index Numbers?

Loose-Cannon

Loose-Cannon

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I figured the members of CGN may find this information interesting..... Please excuse any sksfiles member references because this will be a back/back two post OP containing the subject and then the results in my second post.

Full thread located here. http://sks-files.com/index.php?topic=3767.0


In a recent brain-storming thread located here, the age old topic came up regarding the large corresponding numbers found stamped into the barrel lug and receiver on threaded barrel actions (minus Yugos). Most people over the years have said these numbers were applied to keep the barrel and receiver together when separated. I for one have never bought into this notion and have been convinced these numbers are some type of numbering/measuring system vital for mating barrels to receivers at the factory while ensuring perfect rotational indexing during the assembly process. Admin GM and RM actually had the light bulb go off at the same time without collaboration as to how these numbers may have been used.

We think that the two numbers on the barrel and receiver that you tend to see on every Russian, Romanian, Albanian, and threaded Chinese SKS are in fact rough indexing numbers that the builders used when mass producing those particular components. From all the data RM has compiled, the numbers run from 0 to 35 for a total of 36 different numbers. As there are 360° in a circle, it would seem that each number indicates ~10° variance in the start of the the thread for ease of indexing the two parts together w/o a lot of trial and error.

If we are right on this, then for example a receiver with a #10 would mate to a #10 and index the barrel within 10° prior to torquing. If, however you took and replaced the correct barrel with a #19, I would expect the indexing of the two parts to be approximately 90° off give or take ~10°. A #28 barrel would be 180° off and so forth.

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For reference here is a quote from myself in the brain-storming thread.


Its nearly impossible to clock the starting position of male or female threads even on the most modern CNC machines yet alone in the 50s.

What your looking at is rotational degrees that are plotted prior to mating of the components. You would mark the witness mark 90° from 12 o'clock and thread the barrel into a jig. This jig would have 360° marks all the way around it in 10° increments from 0 to 35. When you seat the barrel all the way into the threaded jig your witness mark will land on a number. You stamp that number which literally plots the beginning location of the first thread. You do the same on the receiver using a male jig and stamp the number.

You now have receivers and barrels on standby numbered 0 through 35 representing the rotational degree of the begging thread. You achieve perfect index every time you match the numbers.

It explains the witness marks, the numbers, and the entire process of how they indexed barrels to receivers.
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So, how can we prove this theory to be fact?

What we propose is that we take two guns from the same country of origin that said numbers are differing by 18 digits which would represent a 180° difference between the two, take the barrels off the receivers, swap both barrels to the apposite receivers, and if we are correct.... We should have two barrels inverted 180° from where they should be when seated. So in short, FSBs and gas-blocks will be facing downward at the 6 o'clock position and the stock ferrule facing upward at the 12 o'clock position.

To put this plan into action, we a have recruited none other then SKSFiles long time member and gunsmith Ben Murray of Murray's Gunsmithing to perform the test.

Below, I present to you the test subjects. One is a 1958 Chinese /26\ marked as a 13, and a 1959/60 letter H series Chinese /26\ marked as a 31. These two numbers were specifically chosen by me from my collection because 31-13=18 and this 'should' represent a difference of 180°.

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And just to have a little fun with this, I created this thread as a poll so you can vote whether or not you think our theory holds any water. :) Remember, we could very well be completely wrong and have to go back to the drawing board, but atleast we here at SKSFiles are giving it a try. wink1

Results will be posted in two days on the evening of Friday 12/01/17
 
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Ladies and gentlemen, members of SKSFiles..... We have 180° inverted barrels.

dance2 dance3 locomotive1 ---------------- declare1

For your viewing pleasure I first present to you barrel #31 mounted and torqued on receiver #13. Since the RSBs were loose, we simple rotated them to about where they should align with the rest of the barrel components. The important thing to note is the 180° inverted stock ferrule, gas block, front sight block, and of course the witness marks. wink1


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Now for barrel #13 on receiver #31 we didnt torque the barrel to the receiver. We have ZERO doubt it would have also indexed at exactly 180° also, but we did this to roughly show where mating of the two surfaces began prior to torquing the remainder of the way. BUT, as you can see in the first picture, we hand tightened this barrel and the threads on this one were a bit tight and we didnt get it quite all the way seated by hand. Absolutely no doubt this barrel would have indexed exactly 180° inverted like the other. thumb1

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It is in my opinion these rotational indexing reference numbers would have allowed them to achieve within 20° to 30° PRIOR to index and that amount would be torqued until the witness marks align. When we reinstalled the proper barrels on their respective receivers this is exactly what was observed. wink1


And dont fret.... the rifles are back to normal without a single adverse affect. clap1

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Its nearly impossible to clock the starting position of male or female threads even on the most modern CNC machines yet alone in the 50s
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Pretty sure the Germans, Swedes, Brits, and Americans had thread timing sorted out at least 50-60 years earlier...
 
Of course, using jigs as I have described. As far as mass production repeat-ability clocking the first thread angle without a similar system, not so much. If they were able to do that there would be no reason for these numbers to exist or the theory to have been proven.
sHa_wink3.gif
 
You have clear pics to verify?

Yugos, NKs, and EGs dont either.... they likely utilized a tagging method or possibly an ink mark rather then physically stamping. There are several ways to allocate a number to each unit and store them in corresponding bin numbers.
 
jaroslav said:
My 1949 SKS has NO numbers. What about that? jstin's 1950 SKS in the thread ''1950 SKS with SPIKE BAYONET'' has NO numbers either.
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I do see a '0' on his barrel lug. Perhaps in early years nothing on the receiver meant 0.

Its possible in early years they didnt physically stamp the number.... see post above.
 
Loose-Cannon said:
Of course, using jigs as I have described. As far as mass production repeat-ability clocking the first thread angle without a similar system, not so much. If they were able to do that there would be no reason for these numbers to exist or the theory to have been proven.
sHa_wink3.gif
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In commie Russia/China that makes sense...they were not as advanced as the western nations.
 
More I think about it, more I get confused. Why the receiver and barrel have the same numbers? Would it not be easier to pick say, receiver # 23 and barrel #19 and calculate the degrees? 23-19=4 x 10=40 degrees.
 
jaroslav said:
More I think about it, more I get confused. Why the receiver and barrel have the same numbers? Would it not be easier to pick say, receiver # 23 and barrel #19 and calculate the degrees? 23-19=4 x 10=40 degrees.
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Im sorry, but this comment literally makes zero sense. Whats easier then matching a #23 with a #23? This is the ENTIRE purpose of the numbers as this thread proves.
 
Loose-Cannon said:
Im sorry, but this comment literally makes zero sense. Whats easier then matching a #23 with a #23? This is the ENTIRE purpose of the numbers as this thread proves.
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Probably was more prevalent and perhaps necessary in China where parts were made at different plants and assembly was centralized.
 
If you really wanted to get anal about how this process was executed. We witnessed the barrels mating angle prior to torquing to be in the neighborhood of 20 to 30 degrees. Not only would they have clocked the timing of the male and female threads to establish the index point, they also would have either advanced the index value of the barrel jig, retarded the index value of the receiver jig, or both in order for the barrels to time somewhere between 20 and 30 degrees EARLY and that remaining amount of rotation to index is all torque.
 
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jaroslav said:
I mean, what about if you have odd numbers and can't find a matching pair.
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700+ complete units a day and you dont think they would have bins containing barrels and receivers numbered 0-35.
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In the event they went to get a receiver and that number bin was empty..... next bin. After the next shift that bin could have more then others.
 
Loose-Cannon said:
Thats why the timing indicators are found on Russian, Chinese, Albanian, and Romanian?
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dunno about those others, you only showed it with 2 chinese examples. Other fella says no numbers on his Russians... I have 3 I can check later to see if they have any matching indexing numbers.
 
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