Type 81 build/conversion in 223/5.56 NATO

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romayama

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As I promised to a couple of members, going to post the progress pics of the 223 conversion work.
With the prayer, work has started.
From one of my previous projects I had a take-off T97 barrel which proved to be a good base for this conversion so far. The shank was smaller than the T81 trunnion opening, so it required a press-on bushing. Other than that, barrel diameters where devices were installed are very close, within the +/- 0.001" which was a good surprise for me. If the T97 barrel was not available, an AR15 barrel would be a good candidate.

Donor barrel
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The donor rifle is taken apart. The T97 Barrel is stripped of the devices and has the bushing pressed on.
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The T97 barrel is at the bottom - barrel shank is machined to size, barrel devices are migrated onto it just for the fitment check. On top is the stripped T81 barrel
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Some unused notches for the pins will be filled using welder and then machined flush, just for the aesthetics
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Existing gas port will be reused
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The 223 muzzle. Planning to put back the "bird cage" T97 flash hider on it when finished
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To be continued
 
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After taking a day pause, I had following thoughts on the gas system length:

Many great rifles in 5.56 including that rare T81/5.56, T97, M-16, AR-180 and e.t.c have the rifle-length gas system for a reason - it is related to the slower burning rate of the 223 powders compared to their intermediate counterparties used in 7.62x39 and 300blk. Generally speaking, current carbine-length gas system with large piston most likely will overgass the rifle, while rifle-length systems generally work smoother with the cartridges like the 223 and 308.
My current thoughts are to move the gas block forward, to take advantage of the existing gas port which is also a rifle-length.

Pros:

- Smoother operation
- More authentic look
- No risk of peeling chrome liner when drilling a new port. I gather that the bores are chrome-lined at the factory after ports were drilled.

Cons:

- Need to lengthen the op-rod and op-rod cover

Cons are fairly easy to overcome, so this is the way I am thinking of proceeding

Original T81 in 5.56 with the rifle-length gas system (TFB)
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If you are committed to using the Type-97 barrel, then lengthening the gas system might be the way to go. If the gas port on the Type-97 barrel is too large for some reason, then you can always use the "0" setting on the Type-81 gas plug as a way of slowly working up the gas volume, by drilling it and slowly working up the diameter of the hole until you achieve the level of function/reliability you desire :)
 
b-wingpilot said:
If you are committed to using the Type-97 barrel, then lengthening the gas system might be the way to go. If the gas port on the Type-97 barrel is too large for some reason, then you can always use the "0" setting on the Type-81 gas plug as a way of slowly working up the gas volume, by drilling it and slowly working up the diameter of the hole until you achieve the level of function/reliability you desire :)
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Yes, and I think this is the easiest approach as well for somebody starting with the AR barrel or blank, keeping the carbine-length system. AK/Krink in 5.45 is a working example of the short system and smaller orifice. In my project I was thinking of maybe welding the existing orifices shut in the regulator and re-drilling as per your suggestion of tuning
 
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Blastattack said:
How are you overcoming the difference in case head diameter? Of main concern are the bolt face itself and the extractor.
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After exchanging ideas with b-wingpilot, it seems like bolt face reduction ring will be pressed in and silver soldered using fine torch, then machined to size. Cutaways will be done after, for the extractor and ejector. Making extractor to come closer to the center should be easy by just removing a bit of metal
 
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Love the idea of moving the gas system to rifle length, thank you for posting all this and sticking to your “guns” on the project.

You are a real red rifle rock star!
 
I thank you Guys so much for the words of encouragement, that is extremely kind of you!

My "shop" with the welder has been deenergized for days so unfortunately I need to wait until it is back in the game, to continue with the "meat and potatoes". I however was able to finish a bracket for the Magpul forestock in the downtime. Yay or Nay to the polymer furniture on red rifle?

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Working on the bolt face today. Started reduction ring from the steel nut. 223 case head is about 2mm smaller than the 7.62x39. B-Wingpilot suggested to use high tensile strength soft solder from Brownells, to affix it to the bolt. I could not find the product in Canada, so my friends in the US will send me one. That may take up to two-three weeks though.
Excess metal from the ring gets removed afterward

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Curtton said:
i was looking for silver solder last year and that was difficult to find too. im still looking.
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Silver solder is sometimes available through the welding supply shops, fluxed and non-fluxed, that is where I get mine all the time. A concern with silver solder/brazing is that it requires hi-temp torching, almost to a cherry-glow. I don't think the locking lugs are hardened, but just in case would like to stick to the low-temp, high-strength solder.
 
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