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Discussion Starter · #1 ·
Ok, finally got to take the 99 out for shooting today and ran into some problms.

1) original barrel converted by Bob Naess to 308. The gun on the lowest gas setting would rip rim off the round where the extractor grabbed it. When a cleaning rod was used to clear the round it popped out easily and has no marking from the chamber. Any suggestions gang?

2) 7.62X39 Jim Langley conversion kit, ran fine and fed fine but would run 1 round longer after the trigger was released. Not sure if this is normal with the Jap 99 or not. No gas adjustment on barrel block with his conversion. Comments?
 

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I don't have a Jap LMG in front of me but it seems that it has a hotchkiss like gas system if I recall properly. That means unscrewing the adjuster allows more gas to escape and reduces the pressure in the system. I may have this backwards but its worth looking at carefully to make sure you are really on the lowest setting. One thing to try is oiling the cases too. Don't over do as light is as good as heavy and won't gum up the guts. It has been said many times that there is no primary extraction with the jap guns but if you look at the locking system you will see that there is a slight amount of movement as the bolt unlocks. It may not be quite enough if the gas is up high though...


The langley conversion may be a tad short on gas to operate and its just barely catching the sear when you let go of the trigger. That might allow that extra round. I have no idea how you can pump that pressure up to make sure.

Just guesses on my part since I'm not the jap gun guy....

Frank
 

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Here is a video of it shooting the 7.62X39.

http://www.youtube.com/watch?v=vt3VkQG-Xps

you can see it run away for a few shots in the video.
Mongo,

Saw it and it looks nice. Couple of thoughts on the firing after letting up
on the trigger.

1) Insufficient gas pressure.
2) Sear is not rising fully.
3) Sear is worn, rounded and/or sear spring is weak.

It seems like the op rod "wants" to catch on the sear and then it lets go.

Take the small square plate off the bottom of the trigger group (just in front of the trigger area). While the plate is off, get the sear and spring out and get in there with some solvent to make sure there is no gunk in there to impede the sear rising when you let up on the trigger. Make sure the sear does not appear worn. Try another sear/spring combo if you want to; they should pretty much be interchangeable unless you have a late sear as a replacement (they are not cut for the sear safety and can't be used with the sear safety in place.)

Type 96 LMG
 

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Discussion Starter · #5 ·
I have taken it apart before the shoot to check it since the safety for the locking block was sticking. The sear spring is pretty weak and the sear looked pretty good but I'll check that better. Maybe the 99 op rod will help this issues as well.

What are the two have rounds on the front of the trigger housing for anyway? I could not figure that one out.
 

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I have taken it apart before the shoot to check it since the safety for the locking block was sticking. The sear spring is pretty weak and the sear looked pretty good but I'll check that better. Maybe the 99 op rod will help this issues as well.

What are the two have rounds on the front of the trigger housing for anyway? I could not figure that one out.
Fair point and worth a try. If you are still running the T-96 op rod, swap out that with one of the spare T-99 rod and bolt assemblies you have. Since you mentioned the spring is weak, that seems a good (and simple) item to swap out first.

As I understand it, at one point very early on in the T-96 series, there was a hole drilled through the half rounds which allowed some type of mounting pin to fit the LMG to a tripod. I usually see them slightly dented from banging into things. Anyway, that's what I've heard... FWIW, on late T-99 trigger groups, the half rounds and the sear safety/ safety channel were deleted.

Looking forward to another update.

Type 96 LMG
 

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My bet is the sear spring. I would try that first with the 99 op rod and bolt.

Once you get the wrinkles ironed out the 7.62x39 barrel combo is a ton of fun!

As for the 7.62 barrel I had the exact problem getting mine to run with 7.62 NATO. I don't know who made my barrel (came with the weapon) but I think it is the same as yours, M60? barrel liner in a org. 7.7 barrel? My problem was a headspace. Once again try the 99 op rod and bolt and double check the HS.
 

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Good videos Sam. I watched the video you linked to subguns and I'm with CR Junkie on this one. It looks like a sear or op-rod problem in the 7.62X39. Its a cool runner too.

As for the .308 I'd be careful not to do anything that will allow the op-rod to hammer the back of the receiver any harder than it does. Cutting mainsprings or substituting lighter springs may sometimes fix a symptom but invariably leads to more damage somewhere else. If the gun won't run with the spring thats in it something else is wrong. Putting a stiffer spring in shouldn't compromise running it should just speed it up or at worst prevent the sear from catching. I'd work with the gas system to reduce the pressure and check headspace carefully.

Good luck
Frank
 

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The Japanese Type 99 gas adjustment operates by throttling the gas entering the gas cylinder from the barrel port, not by metering the exhaust. There is a scribe mark on the left side of the gas block, at about 11 o'clock, with which the gas adjustment spindle is indexed. The spindle has five numbered and detented orifices of different diameters that can be rotated into alignment with the larger barrel port. The smallest orifice (the least amount of gas) is Number 1, and the largest is Number 5. Since the spindle is threaded and bottoms out at Number 1, opening it to a higher setting slightly increases the volume of the gap in front of the piston head, which also tends to boost the available energy.

There can be little doubt that the T99 does employ primary extraction. The front wall of the locking recess in the bolt is not vertical, but is cut on an angle that is easily seen in profile. This allows the bolt to move backward slightly as the locking block is withdrawn, before unlocking is completed.

This design was very well thought out, and the gun was admirably suited to the combat conditions in which it served. It is rugged, accurate, well closed-in against the elements, reliable and easy to disassemble and maintain, superior in many respects to the BAR. A U.S. Army veteran of New Guinea and the Philippines related to me that his unit made it SOP to reinforce their own line with every T99 and T96 they could capture; the only limitation being sufficient ammunition.

M
 

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Sorry to hear that you are haivng troouble with the .308 conversion barrel. Give me a call if you want and we can talk about it. One thing to look at is if the ports in the regulator have been enlarged. I've had a number of barrels through here with ports that were drilled out to overcome some problem with the barrel, usually chamber pitting or pitting left over from welding that was removed. I odn't recall your barrel's chamber, but the barrel teste din one of my guns.

Bob
 

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Discussion Starter · #14 ·
Bob, I took a closer look at the barrel and noticed that the carry handle was actually hitting the receiver and not allowing the barrel to seat all the way back on the shim. I see how you converted the barrel by setting the shoulder forward and moving the gas block forward as well. It looks like you modified the carry handle. I am going to grind it a little bit more to clear the receiver and recheck the ehad space. I'm also going to switch to the T99 op rod and bolt. The barrel did not come with a gas regulator so I used one from my original barrel. I checked the gas ports and they have not been modified (I have 3 gas blocks to compare). It was set on "1" as the lowest gas setting. I don't think the exctractor was fully seating on the rim and might be part of the cause. I'll let you know.
 

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Discussion Starter · #15 ·
Ugh, tried the gun out again today in 308 and it was a no go. I did not bring any other barrels so it got stuffed into the car. Bob, I'll be giving you a call soon to discuss the barrel and to see if you can help me out. I think I know what the problem is but would like to talk to you about it before I post.
 

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If the T99 barrel hole dia for gas porting and the 5 hole dias in the gas adjustment spindle can be measured without a lot of trouble, would one of you mind either posting or emailing me the measurements? I need those dimensions as a reference for calculations on another project I'm going to start later this year. I know it's hard to measure small holes without the right tools, but all I need to know is the largest size bit, for example, the holes will pass. That'll get my project started. No matter what, I still have to do the CFD analysis. Thanks!
 
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