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Thread: Omega Man MK-760 problems

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    Happy Camper hcpookie's Avatar
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    Default Omega Man MK-760 problems

    I'm not a tube gun expert.


    My friend's MK-760 (clone of the Omega Man's SW-76) is having some feed problems.

    The firing pin hits ***very deep*** when it hits, so we know the firing pin is not the problem per se. These are known for poorly built firing pins made of soft metal that peen themselves down and cause light primer strikes. When it malfunctions, there is an ever so shallow mark on the unfired round.

    After doing some research, it seems that the magazine tolerance on these is VERY close to the point that the magazine feed lips may be touching the bolt sometimes, causing feed issues. I have some Suomi magazine conversions we're going to take along to see if other magazines suffer the same problem.

    It was about 30 degrees outside. I'm not sure if cold cold weather can affect the performance on these tube guns... it wasn't the cleanest weapon I've ever fired... is it possible some grease was thickening up and causing the action to hang?


    Curiously, the Wolf 9mm we used seems to malfunction the most. Both stovepipes and failures to fire. It seems as if the striker is not resetting. Every single one of the rounds that would not fire in the MK would fire fine out of my Uzi. So we know it is not the ammo.

    When we used some reloaded 9mm, we got consistant performance with only some stovepipe issues.



    SO.

    Are we missing anything? I'm taking the power inverter and dremel with me to make on-the-spot mods at the range.

    Based on previously published info, we're going to examine the magazine and sand those down if they are contacting the bolt.

    We gave it a THOROUGH cleaning so we can rule that out completely. The blowback on this one really fouls up the magazine and chamber, more so than even my Uzi!








  2. #2
    Happy Camper hcpookie's Avatar
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    wow I guess no one has tube guns although I can't blame them

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    GuncoHolic kernelkrink's Avatar
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    We need more info! Every gun is different, so "tube gun" is like saying "Semi auto rifle", an AR is gonna be a different diagnosis flowchart than a Barrett 50.

    MK760 is the open bolt full auto? If so it shouldn't have a striker it should have a fixed firing pin in the bolt and the bolt slamming shut should fire it. If it is a semi auto it should have a striker and the bolt hanging up on the feed lips might cause a fail to completely close, which would mean a Kaboom in a striker fired design, or a failure to fire due to the disconnector not releasing yet. On an open bolt it would just result in a misfire.

    So what are we dealing with here?

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    Gunco Regular The Dark Knight's Avatar
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    It could be with the striker (and possible a new spring) the blow back of the shell doesn't have enough power to eject the shell completely.

    Does the bolt hit the back of the receiver?

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    No Hope For Me Coils's Avatar
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    Like Kernel said, need more detailed info.
    You said you had a few that didn't fire even though you heard the striker click. Was there any marks on the primer?
    As for the stove piping, how many rounds have been fired? If not many, it could need a break in type thing?
    "Government is not the solution to our problem, government is the problem" Ronald Reagan

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    Happy Camper hcpookie's Avatar
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    OK I apologize for not being more detailed - I made some generalizations based on my ignorance of this weapon.

    I do know it wasn't just dirty or a magazine problem - a thorough cleaning and careful filing of the magazine lips and it still malfunctions. He left it with me so I can take it apart and look at it more closely.

    It is indeed a semi-auto only, striker-fired tube gun. Similar to my uzi in comparison. The gun is historically known to have firing pins built from soft steel causing premature firing pin wear and failure. This one seems to have had that corrected as the firing pin is so long that it DEEPLY impresses the primers. So the previous owner already fixed that issue This is my friend's 2nd MK-760 and the first one he had did have the weak firing pin issue. The magazines are sometimes known to drag across the bottom of the bolt, which is why the filing was done. Either of these issues don't apply to this gun.


    More careful observation after the last malfunction suggests the extractor is not always grabbing the rim. We observed light primer strikes which was confusing due to the "extra long" firing pin. We were able to repro the light primer strikes by slowly pushing the bolt over the magazine, stripping off the round, but NOT pushing the bolt into battery. At that point, the extractor does NOT grab the rim. Do that enough times and the pin will sometimes lightly tap the primer but not fire. That seems to be the condition.

    The question is what causes this condition. It appears that the extractor may be sticking or possibly have a weak spring causing it to fail to function, in turn preventing the bolt from completely moving into battery. We therefore plan to disassemble the bolt and give it a careful examination.

    The flip side is that perhaps the main spring is too heavy ? causing the bolt to fail to reset the striker. Or possibly that the sear is worn to the point that it doesn't reliably engage the striker. Or that the striker is worn and can't reliably be disengaged by the sear. If any of these are the issue, then the light primer strikes make sense.

    Bottom line, sear or extractor. That's all I can guess for now. These things are pretty simple toys so there isn't much else it could be I need to make some time to sit down and examine it more closely.

  7. #7
    No Hope For Me Coils's Avatar
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    More careful observation after the last malfunction suggests the extractor is not always grabbing the rim. We observed light primer strikes which was confusing due to the "extra long" firing pin. We were able to repro the light primer strikes by slowly pushing the bolt over the magazine, stripping off the round, but NOT pushing the bolt into battery. At that point, the extractor does NOT grab the rim. Do that enough times and the pin will sometimes lightly tap the primer but not fire. That seems to be the condition.

    The question is what causes this condition.
    Extractor
    A friend has an Kimmel ap9 (TEC9 knock off) and it was doing the same thing, I didn't notice it until we tried some CCI aluminum cased ammo and saw then dent in the rim of the case.
    I'd guess it's the angle (or lack of it) on the end of the extractor that pushes the extractor to the side to let it go into the grove on the case. I filed this area to make this taper a little longer.

    In case I'm not explaining it very well again
    The black is basically how his was and the red line shows how it was filed to extend the ramp.
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    "Government is not the solution to our problem, government is the problem" Ronald Reagan

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    GuncoHolic kernelkrink's Avatar
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    Probaly the extractor needs modified as Coils said. I would also put a radius on the bottom like a 1911. Does the boltface have the bottom feed lug on it like the FA, or is it flat? If the striker is following the bolt forward you will either get FA fire (feed lug intact) or a jam (lug missing) as the case jams under the extended FP.

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    Happy Camper hcpookie's Avatar
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    Coils the extractor mod functioned perfectly! He finally bought some more 9mm and ran a few mags through it yesterday with no hiccups.

    The extended FP seems to be a moot point on his gun. These guns are notorious for having soft firing pins, so this one may have been modified as a result. But it works!

  10. #10
    No Hope For Me Coils's Avatar
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    That's great, I'm glad to hear it was a simple fix.
    Hopefully he got one with a good firing pin, that would suck to finally get it running and the firing pin breaks
    "Government is not the solution to our problem, government is the problem" Ronald Reagan

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