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Old July 07, 2019, 18:58   #1
Naga1337
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New build FTE, and some ideas

Hello everyone. I've been out to the range three times with a new FAL build, and haven't had much luck getting it to run correctly. The kit is based primarily on a Rhodesian parts kit. However, the receiver, barrel, front sight base with brazed gas tube, locking shoulder, and bolt are DSA parts.

Initially, the casings were sticking in the chamber to the point that the rims were getting ripped off the casings, but some chamber polishing solved that issue. Now, the issue is failure to fully cycle. The bolt carrier group slides freely in the rails, as does the gas piston in the gas tube. When firing, sometimes it ejects the casings, but other times it fails to eject the casing, and it tries to put it right back into the chamber. I have been unable to get it to lock open on an empty magazine when shooting, and I have tried it with multiple magazines. Slow motion video with my phone camera shows that when it fails to eject, the bolt comes back only about halfway before returning forward.

I have noticed some evidence of powder fouling around the gas block area. I have tried finding leaks by placing masking tape on the various areas and shooting it. Today, I put some masking tape on the top of the gas regulator knob along the front where it tightens against the gas block, and discovered that when it is fully closed, enough gas is leaking around the regulator knob that it blows the masking tape off.

My thought is that possibly this regulator knob, which is a surplus part, is slightly larger on the inside than the gas block journal it screws onto (the gas block being a DSA part,) thus allowing gas to leak around it even when fully closed. I have also noticed that my gas regulator knob is easy to turn by hand, while I notice the normal complaint is that it is too hard to turn, requiring the wrench to turn it. This would seem to lend credence to the theory that it might be a loose fit.

Does anyone have any thoughts on what might be going on?
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Old July 07, 2019, 19:14   #2
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You definitely have a lack of gas, but I am struggling to believe the gas nut would be the culprit. I have no experience with DSA parts however so???

Barrel length? Gas port size? I would start there if it were me.
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Old July 07, 2019, 19:22   #3
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Originally Posted by Invictus77 View Post
You definitely have a lack of gas, but I am struggling to believe the gas nut would be the culprit. I have no experience with DSA parts however so???

Barrel length? Gas port size? I would start there if it were me.
Hi. The barrel length is full length. Gas port size is whatever it came with from the factory. I have not measured it. I wrapped tape around the barrel in front of and behind the gas block, as well as around the gas tube just behind the gas block, where the brazed joint is. None of this tape appeared to gather any powder fouling. The only area the tape did anything is when placed at the aforementioned location, above the vent when the gas regulator is fully closed.
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Old July 07, 2019, 19:26   #4
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Interesting you mention chamber polishing to keep it from a case head separation. Ya think something may still be wrong in the chamber? If you can snatch a case head off before polishing a chamber maybe something else is awry. As in the cases were stuck before and now not quite as stuck.
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Old July 07, 2019, 19:30   #5
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Interesting you mention chamber polishing to keep it from a case head separation. Ya think something may still be wrong in the chamber? If you can snatch a case head off before polishing a chamber maybe something else is awry. As in the cases were stuck before and now not quite as stuck.
Hi. I did not see anything obvious looking in the chamber or looking at the fired cases. I have an endoscope that might let me get a better view in the chamber. I can try this out tomorrow.
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Old July 07, 2019, 19:31   #6
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As in the cases were stuck before and now not quite as stuck.
Interesting point.....
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Old July 07, 2019, 19:36   #7
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Hi. I did not see anything obvious looking in the chamber or looking at the fired cases. I have an endoscope that might let me get a better view in the chamber. I can try this out tomorrow.
Look at the brass. I'm not an expert. Get another regulator cuz they're cheap if you suspect something there. My point is that snatching off a rim and now can't extract makes me scratch my head.
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Old July 07, 2019, 19:41   #8
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Have you checked correct orientation of gas plug?
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Old July 07, 2019, 19:44   #9
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Have you checked correct orientation of gas plug?
Hello. I'm not sure what you mean. The angled cut that allows me to adjust the size of the vent in the gas block is facing forward, so I can adjust the size of the opening.
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Old July 07, 2019, 19:49   #10
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Have you checked correct orientation of gas plug?
To the best of my knowledge, the gas plug is like people. Male or female. Shoot or grenade.

I don't believe the gas plug can identify as any other orientations.

I could be wrong. YMMV,
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Old July 07, 2019, 19:52   #11
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Originally Posted by Invictus77 View Post
To the best of my knowledge, the gas plug is like people. Male or female. Shoot or grenade.

I don't believe the gas plug can identify as any other orientations.

I could be wrong. YMMV,
I see what he means now. It is open.
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Old July 07, 2019, 21:15   #12
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Are the recoil springs and tube clean and lubricated ?






.................................
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Old July 08, 2019, 06:03   #13
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What are you using for ammo ?
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Old July 08, 2019, 08:30   #14
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Similar thing happened to me but my problem was with an 18" barrel. I polished my chamber with 600 grit paper and opened my gas port to .115. It runs like a champ now. You didn't state what barrel length you have but I'm assuming with a Rhodesian kit it is 21". I believe port size on those are .98-.100. Try running a bit through the port to clean it up and see if that helps. I wouldn't go too oversized at first. Go in small increments.
Hope this helps and good luck
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Old July 08, 2019, 08:45   #15
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Just reread post. Saw where you mentioned barrel length.
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Old July 08, 2019, 09:04   #16
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Quote:
Originally Posted by tdb59 View Post
Are the recoil springs and tube clean and lubricated ?






.................................

Extremely valid question here as well. Clean tube & spring and LIGHTLY lubed.
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Old July 08, 2019, 20:34   #17
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Hello all. Thanks for the ideas. I will provide some more information.

The first time I had the rifle out (when it was bending/tearing off case rims,) I noticed that after removing the stuck casings, they had sort of dull streaks on them running along the axis of the case. The streaks could be seen but not felt. I polished the chamber with Mothers Mag and Aluminum Polish on a chamber mop, spinning it in the chamber with a drill for a few minutes. After this, the streaks on the casings stopped appearing, and it no longer tore the rims off the casings. I will see if I can find any of the casings for further inspection. I think I threw them all out, but there might still be some in a trash can.

I also remembered something I tried at one of the previous range trips: I tried oiling a few cartridges with CLP, loading them into a magazine, and firing them, and I recall they extracted and ejected properly. But a few unoiled rounds later, the problem returned

I have tested the gun with grease, oil, and dry (that is, wiping off the oil with a dry cloth, not actually cleaning it off chemically) recoil tube/plunger, with no discernable difference in function. On a related note this most recent time out, I saturated the bolt carrier, rails, and hammer in oil, but it did not seem to help.

For ammunition, I have tried Prvi Partizan M80 in a white box, as well as IMI 175gr Match 7.62x51. Interestingly, the Prvi Partizan leaves a brownish soot residue when fired, which helps track where the gas is going.

I don't have a good tool to check the size of the gas port in the barrel, but it does not appear to be obstructed or anything. I will look into getting some drill bits of appropriate sizes to use as gauge pins, and to drill it out larger if necessary

A few other things I didn't think to mention previously, and another observation: All the springs, as well as the gas piston itself, are new DSA parts. The gas plug is a South African gas plug with grenade sight. It appeared to be unused when I received it. I noticed today that the paint on the rear of the grenade sight, where it rests nearest the gas knob when folded, appears to have been blasted off. I compared this to a used grenade gas plug that I have, and it does not appear to have this issue.

My endoscope battery is dead, so I was unable to check the chamber with it. However, a visual check did not reveal anything particularly unusual.
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Old July 09, 2019, 15:24   #18
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oiling cartridges is a very bad idea. it allows the case to slide backward early in the pressure curve created by the expanding powder gasses, and can wreck a good rifle by increasing bolt thrust to dangerous levels. very few guns are designed to run oiled cartridges. (Breda machine gun, for example)

go to your local hardware store and buy number drill bits in the 30-39 range, and a cheap dial caliper (or just read the below linked chart for diameters), and you can measure your gas port after removing the front sight. in 21" bbls should be around .105", and in 16" may best function as big as .125"

https://littlemachineshop.com/refere...rdrillsize.php
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The next time I hear "THE RANGE IS NOW HOT", it just wont be the same.

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Last edited by justashooter; July 09, 2019 at 15:31.
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Old July 09, 2019, 15:28   #19
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Quote:
Originally Posted by Invictus77 View Post
You definitely have a lack of gas, but I am struggling to believe the gas nut would be the culprit. I have no experience with DSA parts however so???

Barrel length? Gas port size? I would start there if it were me.
dial caliper can measure ID of socket and OD of plug. you want about 5 thousandths of a inch clearance.
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If the concept of heading on down to the local Home Depot and transforming $100 worth of random pipe bits into a killing machine doesn’t appeal to you, you’re a frikkin' pansy. Also, you’re probably sane and will live significantly longer than I will.

Nonetheless you disgust me, and I take comfort in the knowledge that your obituary will be nowhere near as humorous as mine.


The next time I hear "THE RANGE IS NOW HOT", it just wont be the same.

Max tried another question. "What sort of people live about here?"
"In THAT direction," the Jin said, waving its right paw round, "lives a Han: And in THAT direction," waving the other paw, "lives a Ming Hare. Visit either you like: they're both mad."
"But I don't want to go among mad people," Max remarked.
"Oh, you can't help that," said the Jin: "we're all mad here. I'm mad. You're mad."
"How do you know I'm mad?" said Max.
"You must be," said the Jin, "or you wouldn't have come here."
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Old November 23, 2019, 23:06   #20
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Hello again everyone. Sorry for bumping this old thread, but I wanted to update everyone with my progress.

I tried a few things, and the gun is now working, but is still experiencing occasional failures to eject (it rechambers the spent casing.)

I tried lubricating some cases with oil, and the gun seemed to work with these lubricated cartridges. Switching back to unlubricated cases, the gun shortly began malfunctioning again. I polished the chamber, but this did not solve the problem.

I bought a new gas adjustment knob and used a set of calipers to compare it to my old one. I discovered that the new one was, in fact, significantly smaller in ID than the old one. I forget offhand what the old one was, but the new one is about 0.006" larger than the OD of the gas vent journal on the gas block. Installing this, the gun began working. A setting of 3 seems to work with Prvi 7.62x51, but it still experiences maybe 1-2 failures to eject per 100 rounds. I may be able to use an even lower number gas setting and get it working reliably, but based on what I have read from others, I should be experiencing reliable function by now.

Gas piston is from DSA and measures ~0.4300".

I decided to take some drill bits and use them as pin gauges to check the size of the gas port in my barrel. I discovered that the largest bit I can get to fit into the gas port (just barely fitting) measures 0.0925". I read that the Belgian spec gas port size for a metric FAL is approximately 0.1000", but I am not sure if this is accurate. What is the correct gas port size for a metric FAL? Is my gas port undersized?

Thanks.

Last edited by Naga1337; November 23, 2019 at 23:22. Reason: Correction + addition.
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Old November 24, 2019, 12:29   #21
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Barrel's Gas Port specs in 0.089"~0.093" for full size or 21" barrel. Your barrel may be within spec, but undersized in my estimation and should be closer to 0.098", a #40 drill bit.
I believe Mark at ARS says .096"~.098"

Your symptoms are classic lack of sufficient gas. Your rifle is actually running quite well, but you should close the Gas Port to direct more gas to the Piston. Your DSA Piston at 430" is good.

Privi ammo is a bit anemic in most calibers I've tried and likely require more gas than most Milsurp.

Please stop "lubricating some cases with oil".
It raises merry old hell with chamber pressure for one thing.

If you ream your Gas Port, do it in small steps being very careful to not snap off a Drill bit in there.
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Last edited by MAINER; November 24, 2019 at 12:37.
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