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Old March 15, 2018, 07:00   #1
Nathaniel01
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Please explain "Bolt Over Base" Malfunction

Built my first FAL and now tuning it.
Not sure this is my malf, but I read about it a lot here.
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Old March 15, 2018, 07:33   #2
meltblown
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basically the bolt rides over the round instead of catching it and chambering
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Old March 15, 2018, 11:46   #3
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Can be caused by a weak mag spring, bolt velocity too high (recoil springs to stiff), the magazine not sitting in the receiver correctly, or narrow feed lips in the receiver. Probably a couple other causes, but I need more caffeine to get the thinkin' cap on.
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Old March 15, 2018, 12:04   #4
Nathaniel01
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This is the malfunction I'm having.

Only put a few rounds through it before we left for church last night, but I'll be working on it tonight.
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Old March 15, 2018, 12:25   #5
meltblown
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Common with Korean and DSA mags.
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Old March 15, 2018, 13:53   #6
J. Armstrong
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Give us more details about the rifle and the ammo you're using, may help in diagnosing.
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Old March 15, 2018, 16:00   #7
Nathaniel01
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Imbel 18" kit on NOS Imbel receiver.
Magtech .308
Not sure what mags these are, I have a mix- would have to post pics for ID.
Heading home to the range soon.
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Old March 15, 2018, 16:18   #8
J. Armstrong
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Okay, that most likely rules out a bad receiver.
Has the gas been adjusted correctly ?
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Old March 15, 2018, 17:04   #9
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Adjusting the gas seems to have helped deal with the problem in my rifle. I was getting BOB malfunctions during the last 5 rounds of the magazine on most magazines, typically after every 2-3 magazines worth of shooting, most frequently the second from last. I accidentally moved the gas regulator and they stopped happening. I was trying to figure something else out and opened up the gas a bit and got another BOB malfunction. Turned the gas back up one click and it hasn't happened for over 300 rounds.
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Old March 15, 2018, 17:14   #10
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Quote:
Originally Posted by bigstick61 View Post
Adjusting the gas seems to have helped deal with the problem in my rifle. I was getting BOB malfunctions during the last 5 rounds of the magazine on most magazines, typically after every 2-3 magazines worth of shooting, most frequently the second from last. I accidentally moved the gas regulator and they stopped happening. I was trying to figure something else out and opened up the gas a bit and got another BOB malfunction. Turned the gas back up one click and it hasn't happened for over 300 rounds.
Exactly. I tend to run mine at minimum gas just to keep wear to a minimum, and BOB malfs are sometimes the results just as you say.

Of course there are other possibilities but its best to eliminate the simple potential causes before moving on to the more unusual suspects.
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Old March 15, 2018, 19:32   #11
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Gas ring was a revolution too loose. Butted it up to gas block and opened 4 clicks and it now cycles.

It won't pick up a round from the right side of the mag to start with, i.e. 3 or 5 round mag is inserted.

Had two instances of out of battery fire on last 2 rounds in mag but not consecutive mags.

Main testing was with new Moses mag, but tried a few others with same results- not feeding from right side

Bolt is sluggish going forward- I'm not riding it. Sometimes won't close all the way. Moves easily without magazine.

Fired about 25 rounds tonight.

Tested with some Serbian white box from a green plastic battle pack (love that stuff).

Last edited by Nathaniel01; March 15, 2018 at 20:04.
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Old March 15, 2018, 21:30   #12
J. Armstrong
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While it doesn't sound like the cause of your problem, gas adjustment is as follows:

Remove mag and clear weapon. Close gas, in your case maybe another two clicks. You want the weapon to cycle and feed. Load one round in magazine. Load and fire the weapon. It should lock the bolt back. Open gas a click or two - repeat until the weapon does NOT lock back. close one click and repeat, one click at a time until the weapon locks back, then close two clicks for positive function.

This is a little backward from the procedure seen in most manuals, but it avoids ( or at least minimizes ) having the weapon try to rechamber a spent case and the consequent annoyance of clearing the stuck case.

I would also remove and clean the recoil springs, they sometimes get clogged with old, dry lube or have been overlubed and hydraulic lock. With a sluggish bolt, I would suspect the first possibility, although normally this malf won't be specific to either feed station.

The OOBs are a bit more concerning. What are your symptoms ?
If it is a true OOB, it is of course potentially dangerous.
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Old March 15, 2018, 21:38   #13
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Quote:
Originally Posted by J. Armstrong View Post
Okay, that most likely rules out a bad receiver.
Don't you believe it. I had an Imbel receiver that would only feed reliably with one magazine. I believe the problem was how the ejector block was located in the receiver.
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Old March 15, 2018, 22:02   #14
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Boy, if I'd ever heard of that before, I'd totally forgotten it - thx for the reminder Still, not all that commo, though ( unless I've REALLY been asleep ).
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Old March 16, 2018, 05:42   #15
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OOB (?) happened twice with last two rounds in mag. Fired one expected round and rapidly got two, pretty sure before the trigger reset, and then bolt locked back on empty mag. Did not occur every time (I was only putting a few rounds at a time in the magazine). Maybe it was bum p firing, but I doubt it.
I'm going to look at the H,T,S later this evening to check the rake angle.

Is it normal for these riFals to not like to pick up a round on the right side of the mag when loading? It feeds them fine once it gets going.
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Old March 16, 2018, 07:19   #16
J. Armstrong
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Maybe a slam fire - disassemble the bolt and remove and clean the firing pin and check for burrs. Could the trigger and sear springs have been inadvertently swapped ? Are the engaging surfaces of the hammer and sear in good shape and clean ?
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Old March 16, 2018, 09:48   #17
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Get two good-condition Belgian or Israeli mags, and test for 100 rounds.

Other OEM mags can be good too, but other than Belgian or Israeli, hard to find in near-new condition.

Sounds like you have a mish-mash of god-knows-what for mags.
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Old March 16, 2018, 10:59   #18
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They will double if you do the squeeze the till it surprises you
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Old March 16, 2018, 12:14   #19
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Come again?
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Old March 16, 2018, 12:24   #20
J. Armstrong
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If you squeeeeze the trigger very slowly for a surprise break instead of a smooth "stroke", the rifle can double - basically a bump fire. I've had it happen when I did this and didn't have the butt pulled firmly into the shoulder. It's not an OOB, though.
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“I respect the government only in the sense that I respect any other dangerous predator who views me as food.”

“The consolidation of the states into one vast empire, sure to be aggressive abroad and despotic at home, will be the certain precursor of ruin which has overwhelmed all that preceded it.” Robert E. Lee
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Old March 16, 2018, 13:52   #21
meltblown
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Quote:
Originally Posted by J. Armstrong View Post
If you squeeeeze the trigger very slowly for a surprise break instead of a smooth "stroke", the rifle can double - basically a bump fire. I've had it happen when I did this and didn't have the butt pulled firmly into the shoulder. It's not an OOB, though.
Yep. Forgot to say trigger.
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Old March 16, 2018, 13:53   #22
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Gotcha. I may have unwittingly done that. I'll have more time for testing tonight & this weekend.
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