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Thread: Suppressed Mk18 malfunctions

  1. #11
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    I think gas port size depends on when the barrel was made. I literally just installed a DD 10.3" barrel dated 07/2014 about a week ago and i measured the port size to be .0785" (#47) drill bit. I have installed a Govnah gas block but havr not shot it yet, I am waiting for a SBR tax stamp.

    I don't know about 086" but previous posts I have read have said that DD 10.3" barrels were .082"
    Last edited by black22rifle; 04-09-15 at 04:46.
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  2. #12
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    Interesting because I believe someone at DD recently stated .082 and when I measured one with a pin gage set it was at .081. In any case it is overgassed.

    I wonder if Clint has a port reducer that will work for this set up?

    Quote Originally Posted by black22rifle View Post
    I think gas port size depends on when the barrel was made. I literally just installed a DD 10.3" barrel dated 07/2014 about a week ago and i measured the port size to be .0785" (#47) drill bit. I have installed a Govnah gas block but havr not shot it yet, I am waiting for a SBR tax stamp.

    I don't know about 086" but previous posts I have read have said that DD 10.3" barrels were .082"



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  3. #13
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    Some would say a higher weight buffer. Try an H2 or H3 weight buffer. On my old units new M4's had more open gas ports and H6 buffers. But that was only to shoot a wide variety of pressure rating and grain. It also depends on the twist ratio if it has a direct gas port or is a piston driven system. In my unit the new M4's were ambadextrious but the sheriff's department had the short stroke piston M4's. So there are a lot of variants you have to start somewhere and work your way up if he's using a wide open system in a lower buffer weight trying to switch to a more consistent pressure ammo like lake city xm855 just to test to see if the buffer weight is alright would be a better start and cheaper. if it still hang fires where goods jammed up then I would switch the buffer wait out to around a H4 or H5 maybe even H6. At this point without actually having the rifle physically in my hands the best I can do is guesstimate if it were physically in my hands I could tell you the exact problem with it.

  4. #14
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    H3 buffer and LMT enhanced carrier should do the trick.

    That, or send your upper back to DD and tell them to put a barrel in it that doesn't have a gaping orifice for a gas port.

  5. #15
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    Chances are they would not do that for free though munch, DD has a rather high end barrel. They may replace it but question is will they do so for free. LoL just trying to give him some easy fixes to at least try. Chances are he knows someone that has a higher buffer weight than his own and he should be able to temporarily Frankenstein that part to see if it will fix the problem.

  6. #16
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    Why wouldn't they? If spec is .070 and it is measuring .082+, and resulting in repeated malfunctions...I don't see a reason why they shouldn't fix it. OP shouldn't have to spend more money on a $900 upper to get it to run properly.

  7. #17
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    That is true, I must have missed something in the conversation. Had no idea that was a problem. So ya as long as he has physically not altered the gas block and ports they should replace it free of charge. Well also pending on how long he has had said upper.

  8. #18
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    same setup... went to h3 and it fixed it.
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  9. #19
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    Quote Originally Posted by Iraqgunz View Post
    Interesting because I believe someone at DD recently stated .082 and when I measured one with a pin gage set it was at .081. In any case it is overgassed.

    I wonder if Clint has a port reducer that will work for this set up?
    Clint's port kit would be a very good option. I ended up using it on a very overgassed midlength DD barrel and made a huge difference. I got the gun to run with a .070" port. Wouldn't cycle steel case ammo but ran everything else very well.

  10. #20
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    Here are my $0.02 worth, and I am no expert so take it with a grain of salt...

    First, everything that has been said so far about over gassing is at least partially correct and can/will cause malfunctions. A couple of notes though:
    - most commercial 10.5" (yes I know you have a 10.3" DD) barrels have a gas port in the .08x range (even Noveske's is .082) this is not a manufacturing error, this is done because of all the cheap (non-milspec) ammo that is often used by civi shooters.
    - Crane spec is .070 or .071 (I have read both) and was based on milspec ammo tolerances.
    - Suppressed (to not be overgassed) somewhere in the neighborhood of .05x is recommended when using milspec loads - this is what gives such value to the Govnah or other adjustable gas blocks that allow for optimum unsuppressed/weak ammo unsuppressed/suppressed settings - however I digress.

    If everything was fine the day before (same rifle and ammo, and suppressor used), Occam's Razor would suggest that you considered the specific magazine you were using. Even with +10% springs, and Magpul followers there could be an issue with the feed lips that would cause these malfunctions.

    Lastly, malfunctions aside, I personally use an H2 buffer for enjoyment's sake (H2 came standard in the Colt 6920 SOCOM that I had cut down to 10.3")...

    Hope this helps.

    ETA: Or it could be the select fire lower... in which case you should transfer it to me for swift destruction
    Last edited by ACMcGaha; 04-09-15 at 12:14.

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