Type 81 build/conversion in 223/5.56 NATO

Hi fellow Gunnuts,

This is the parallel build based on LMG/AR-15 barrel w carbine gas length (taken off WK-180). Really, the best parts kit to start with. What I forgot to show - is plugging an existing gas port. I overdrilled it using 1/4" bit to the 2/3 of port's depth and then welded it shut. It is conveniently located right under the handguard retainer - another good sign! Then the blanking sleeve is pressed on top of the journal
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Assembly gets turned to accommodate the retainer
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Retainer gets pressed on it. Its final location will be determined by how deep barrel sits in the receiver and will be adjusted later on
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Pressing barrel in. Receiver must be supported by the trunnion only. Here is my redneck setup. I also make pressing force less than the original Norinco, through smaller differential between parts. Norinco uses like 4-5 tons pressure which I find excessive, when you think of guns where barrels are even switcheable, like RA 96 or Steyr Aug. So I make difference about .010" which makes pressure force 1-1.5 tons, by the feel of it
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They finally got married - Capitalist AR barrel and Communist stamped steel receiver :)))
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Magazine fitment and cycling seems to be working well now. Had to do a bit of non-destructive trimming to the front of the magazine at the end, just a few millimeters off the top. TFB TV also mentioned in their video they had to do that in order to run their factory T81 .223.
Factory latch convenintly remained unchanged. I will show the modified trunnion in comparison to the factory one later.
 
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Awesome progress!!!!! Great and innovative work so far, can’t wait to see how the first shots go. Thanks again for posting all the pics / videos of the progress, I really like seeing all the progress step-by-step. Best thread on CGN by far :)
 
First range report, observations and conclusions:

- It cycles
- Gas port diameter is almost right, maybe slightly on the lower side. Stovepipes happened, which is a sign of either slight undergassing or just casings deflected back into action off something
- Ejection pattern without dust cover is consistent: Back and right, perfect cycling, no stovepipes. With dust cover on, it is forward and erratic. Definitely needs either a trimming of the cover or a deflector
- Accuracy was mediocre but not really indicative, as I only had my bolt-action loads of 73gr left, all plinking loads I spent function-checking and zeroing. 73 obviously is a wrong weight for this twist. For the next outing I will prepare 55gr and 62gr loads and a scope, for true accuracy testing
- Planning to reinstate last round bolt hold-open catch

Example of stovepipe:

Slow-mo operation

Nice landscape and clouds below, on the way down from the range
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Cheers guys!

Since the conversion with the T97 barrel is a pilot project and more of a test rig, as a next step, I am thinking of making an AR mag adaptor for it. The second, parallel LMG project, is benefitting from things I learned not to do, and is coming together much more logic and straightforward. I think it will inherit the AK mag feed system.

Had to pull the barrel out of LMG convert to turn it for barrel devices: cleaning rod retainer and front sight. Also need to shave a bit the sector of the breech, for the extractor. Being an AR barrel, muzzle thread is already there.
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Prelim fitment of parts on the LMG 5.56 convert. From this point things should go fairly fast, as no op-rod lengthening is involved
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Thanks for posting the updates!!!! I'm glad you got it firing and cycling. Is there much contact between the ejector and the base of the 556 cartridges? I had a similar ejection issue on a famae 540 and getting more contact on the base of the cartridge fixed the issue. Trimming the top cover may create a bit of a gap between the top of the carrier and the top cover. I'll try to see if I can get some slo-mo footage of 7.62x39 ejecting from a type-81 for comparison.
 
b-wingpilot said:
Thanks for posting the updates!!!! I'm glad you got it firing and cycling. Is there much contact between the ejector and the base of the 556 cartridges? I had a similar ejection issue on a famae 540 and getting more contact on the base of the cartridge fixed the issue. Trimming the top cover may create a bit of a gap between the top of the carrier and the top cover. I'll try to see if I can get some slo-mo footage of 7.62x39 ejecting from a type-81 for comparison.
Click to expand...

Good tip, Wingpilot! True dat - there has been failure to extract once or twice, over a large bulk of shots - I thought of shaving the extractor so it has more travel inward. Will see what difference it makes to the ejection timing.
So far I thought I would need to trim off about 15-20mm of the cover, based on other slow-mo frames. There is still bolt coverage within that range. I however would like to explore other options, including yours, before cutting it

Unrelated to ejection items:

- Oprod extension bushing got bent a bit. I am replacing the whole oprod with the high-strength stainless solid round bar. Not that it matters for the AR barrel conversions.

LMG parallel project:

- For some reason did not have luck soldering bolt face bushing onto the LMG bolt. potentially thinking of adding more steel using TIG and then micro-bore the excess. Have you done that?
- In addition, found that going the AR mag adapter path is probably best and least intrusive path. Although rock-and-lock has it perks

Was Famae in factory configuration or you did you turn it into something completely different?:)
 
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romayama said:
- Oprod extension bushing got bent a bit. I am replacing the whole oprod with the high-strength stainless solid round bar. Not that it matters for the AR barrel conversions.
Click to expand...

Nice. Another option to consider is making a multi-piece op rod. The original WKs suffered having bent/broken op rods most likely because they were too rigid. Making it multi-part like the original AR-18 adds a bit of "slop" and flexibility which stops the bending/breaking.


romayama said:
- For some reason did not have luck soldering bolt face bushing onto the LMG bolt. potentially thinking of adding more steel using TIG and then micro-bore the excess. Have you done that?
Click to expand...

Oh no. I have been tempted, but I would be hesitant with any bolt that has it's locking lugs at the front. With something like a VZ-58 or FAL, welding on the front of the bolt might not cause any problems with the heat treating in critical areas. But with an AK or AR style of bolt, I would be hesitant haha, unless maybe getting it re-heat treated or something.


romayama said:
Was Famae in factory configuration or you did you turn it into something completely different?:)
Click to expand...

I don't think it was in factory condition, but I'm not sure haha. I got it used, and it had issues. I was faced with either building up the ejector or TIG welding some additional steel to the carrier in order to push it closer to the ejector. I chose the easier path and it worked out haha.
 
b-wingpilot said:
Oh no. I have been tempted, but I would be hesitant with any bolt that has it's locking lugs at the front. With something like a VZ-58 or FAL, welding on the front of the bolt might not cause any problems with the heat treating in critical areas. But with an AK or AR style of bolt, I would be hesitant haha, unless maybe getting it re-heat treated or something.
Click to expand...

Hmmm, why not an SKS then :) Got me thinking now, haha

I bought a bubbaed humiliation of SVT sometime ago, thinking of 308'ng it, maybe can use that technique of bolt face reduction here?
This is what it was
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And this is photoshop of what it could look like in 308, with the 20" barrel
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