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Thread: MK18 Vs. Geissele Super Duty 10.5

  1. #151
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    Related anecdote, Centurion 10.3, 100% suppressed, H2 and Colt spring. 100% flawless function, no noticeable gas to face.

    Same lower, same suppressor, Colt 14.5 upper and that thing spewed gas and carbon all over my damned eye pro and face. I looked like I had just climbed out from underneath a truck after servicing it all day.

    Both uppers had BCM charging handles, one a Colt BCG and the other a Centurion.

    FWIW, if going suppressed full time, the Centurion may well be worth a look. Didn’t get to play with it unsuppressed so can’t provide any insight on that end.

  2. #152
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    Quote Originally Posted by bear13 View Post
    I realize it ain’t Colt/DD/Geissele. But I setup a 10.3 with Centurion barrel. The barrel is a beast and built like a brick shit house. But has a .069 gas port. I have yet to be able to get it to lock back on all ammo and some it will choke on. Running unsuppressed.

    I have tried a H/H2/H3 different springs and a few bcg for the hell of it.

    I switched to a a5 system, going to try a a5h3 buffer. But I think I need to punch the gas port out a little bit on her to be correct. From the people I have talked to a .070 is on the edge as it is for 100% function and I think the .069 is just too little. A .071-.072 would probably do the ticket and still run clean.


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    0.07 is pretty perfect for suppressed/unsuppressed in all weather with 5.56. I mean that's literally the standard in a nutshell that led them to go with that size. And with most mags in most weather, it's going to run 223 unsuppressed, as well. I've never had mine fail to cycle, just to lock back on certain mags with tulammo.

    All that changes when you add a silencer though. Suppressed, they're overgassed. So 0.07 is the max I would ever want to go to under any circumstances, and honestly I'm probably going to end up with a BRT gas tube to convert it to full time suppressor use.

    What you might try is clipping a few coils off an extra recoil spring. That's a non invasive thing you can do to try and cycle everything without a can on it.

    Quote Originally Posted by Don't Tread On Me View Post
    Related anecdote, Centurion 10.3, 100% suppressed, H2 and Colt spring. 100% flawless function, no noticeable gas to face.

    Same lower, same suppressor, Colt 14.5 upper and that thing spewed gas and carbon all over my damned eye pro and face. I looked like I had just climbed out from underneath a truck after servicing it all day.

    Both uppers had BCM charging handles, one a Colt BCG and the other a Centurion.

    FWIW, if going suppressed full time, the Centurion may well be worth a look. Didn’t get to play with it unsuppressed so can’t provide any insight on that end.
    If they have an option with a true 5.56 chamber I think that's probably pretty good advice. Kind of hard to find these days outside of the .gov suppliers, and I'm generally suspicious of modified chambers in SBRs. But I'm generally in favor of port sizing for full time suppressor use. The only time I ever shoot my SBRs unsuppressed is when I'm testing my homemade silencers, and it's truly unpleasant. Not something I would ever choose to do under normal circumstances.

    My one hesitance is that there are lots of suppressors out there all with different characteristics, so you're venturing off into the unknown when you build something out of spec. That's especially true of SBRs, which are way more finicky about these things than your typical mid 16 where you can just randomly throw any AR part on it and have it work. Just something to think about with anything that you might use for home defense. When Crane came up with the port spec for the Mk18 they did a lot of testing in a lot of different environments with a wide range of ammo. They have teams stationed in places that are normally -40, others in places that are 130, and everywhere in between, at elevations from sea level to over ten thousand feet. A lot of people build something and test it in one environment and think it's 100%, then get it in a different environment and find that it's completely unreliable.
    Last edited by okie; 10-24-21 at 04:14.

  3. #153
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    Well this is interesting; in another thread a guy said rumor has it that CAG is dropping the -416 because of supply issues, and buying up big G goodness, URGI possibly. But with SF OBC's. As pertains to this here thread, that will definitely add a new wrinkle, huh? Notice I said rumor; this is totally unsubstantiated gossip from other Geiselle thread. If true, this will make Geiselle the next new hotness, and replace DD. I think this has already happen, judging from high-end gun stores, but it would then be official.

    Again, if true how does this change the argument here? Geiselle would then be a legit choice for your MK-18 build. I would assume most folks would have no problems switching between SD and the issue stuff. Might be one and the same. But to Okie's point, it will be 2-3x more expensive than building your own from late-model Colt goodness. But will probably be the preferred method for most folks. I have a buddy like this. Instead of building with me, he prefers to slap plastic at the store and get the factory build. I've worked in factories: I've seen what goes on in there; I prefer to build my own, thank you very much.

    But anyways, this could be an interesting development. Geiselle Super Duty could become Mk-18/URGI.
    Working for Crossfire Australia, a military rucksack and load-bearing equipment company. Still doing limited design and development of nylon LBE.

  4. #154
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    Quote Originally Posted by okie View Post
    0.07 is pretty perfect for suppressed/unsuppressed in all weather with 5.56. I mean that's literally the standard in a nutshell that led them to go with that size. And with most mags in most weather, it's going to run 223 unsuppressed, as well. I've never had mine fail to cycle, just to lock back on certain mags with tulammo.

    All that changes when you add a silencer though. Suppressed, they're overgassed. So 0.07 is the max I would ever want to go to under any circumstances, and honestly I'm probably going to end up with a BRT gas tube to convert it to full time suppressor use.

    What you might try is clipping a few coils off an extra recoil spring. That's a non invasive thing you can do to try and cycle everything without a can on it.
    .
    I did not think of this. Iím assuming it will help with the stroke since your shortening the length of the spring?

    It does not effect the blowback action? As in weakening the ďspringĒ action.

    I would like it to function without drilling out gas port. Iíll cut a few coils off the buffer spring and see what shakes out.

    I will say it seemed happier with the heavier buffers I tried initially. Seems to have more kickback issues and choke on ammo with the light buffer.


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  5. #155
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    Quote Originally Posted by bear13 View Post
    I did not think of this. I’m assuming it will help with the stroke since your shortening the length of the spring?

    It does not effect the blowback action? As in weakening the “spring” action.

    I would like it to function without drilling out gas port. I’ll cut a few coils off the buffer spring and see what shakes out.

    I will say it seemed happier with the heavier buffers I tried initially. Seems to have more kickback issues and choke on ammo with the light buffer.


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    Maybe the lighter buffer doesn't have enough inertia to strip the next round because it's short stroking? Without knowing more it's hard to speculate. What ammo is it having trouble with, and what is the specific malfunction?

  6. #156
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    When I wuz at gunsmithing school, they said cutting coils was a corky no-no. Better to get a reduced power, full-length Springco product. Just sayin'.

    And this is one of the annual inspection items for me. Any recoil spring more than 1" shorter than stock gets replaced. So it would **** up my check list. ha ha
    Working for Crossfire Australia, a military rucksack and load-bearing equipment company. Still doing limited design and development of nylon LBE.

  7. #157
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    Quote Originally Posted by bear13 View Post
    I realize it ainít Colt/DD/Geissele. But I setup a 10.3 with Centurion barrel. The barrel is a beast and built like a brick shit house. But has a .069 gas port. I have yet to be able to get it to lock back on all ammo and some it will choke on. Running unsuppressed.

    I have tried a H/H2/H3 different springs and a few bcg for the hell of it.

    I switched to a a5 system, going to try a a5h3 buffer. But I think I need to punch the gas port out a little bit on her to be correct. From the people I have talked to a .070 is on the edge as it is for 100% function and I think the .069 is just too little. A .071-.072 would probably do the ticket and still run clean.


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    Youíre tuning the wrong thing. That heavy A5 is just going to cause you more headaches.

    Colt spring, H2 buffer, M855 or heavier 5.56 spec ammo and itíll run.

    Everyone likes to blame the dirt shooter crowd for the big gas ports but I think the ĎUpgrade All the Thingsí mentality around here is just as bad.

  8. #158
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    Quote Originally Posted by 17K View Post
    Youíre tuning the wrong thing. That heavy A5 is just going to cause you more headaches.

    Colt spring, H2 buffer, M855 or heavier 5.56 spec ammo and itíll run.

    Everyone likes to blame the dirt shooter crowd for the big gas ports but I think the ĎUpgrade All the Thingsí mentality around here is just as bad.
    I am curious why the decision is to go straight to an A5H3 when that list of standard buffers isnít working. If the tube is already swapped, Iíd try A5H0 on a stock rifle spring and then work my way up.


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  9. #159
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    Quote Originally Posted by Wake27 View Post
    I am curious why the decision is to go straight to an A5H3 when that list of standard buffers isnít working. If the tube is already swapped, Iíd try A5H0 on a stock rifle spring and then work my way up.


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    The A5h0 is what I went to. I have not yet tried a a5H3. That is on its way.

    Also I have ran multiple types of ammo. The main problem it has now is that it does not lock back. With Norma tac 55grn it will eject a round and smash the round feeding in the ramp. Itís undergassed, I realize this. But I was hoping to try the right combination of buffer/spring. It did oddly run perfect with wwb 55grn.

    It has had a low power spring and regular spring with all H buffers in a standard tube. I went to the a5 upon recommendation and thatís what I run in my full length rifles anyways.

    Believe me. I have done due diligence with ammo and all the standard buffer spring/buffer combos. But at the end of the day I want it to work with all ammos. I know with a can this would be ideal, but I have no suppressor yet.

    I pulled that barrel and threw in a rosco 10.5. I have another setup for a new upper to use the 10.3 with.


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  10. #160
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    Quote Originally Posted by Diz View Post
    When I wuz at gunsmithing school, they said cutting coils was a corky no-no. Better to get a reduced power, full-length Springco product. Just sayin'.

    And this is one of the annual inspection items for me. Any recoil spring more than 1" shorter than stock gets replaced. So it would **** up my check list. ha ha
    Normally I agree, but if it's just to shoot tulammo at the range then I have zero issues with it. If the port is sized properly and you're running the right spring and buffer, chances are you're going to have some potential for problems cycling tulammo, or even likelihood with SBRs. No real reason to deny yourself cheap training, so just pop that clipped spring in there to practice at the range, then change it back out. Real cheap and easy to swap in and out, and certainly a better solution than opening the port more than necessary. You can pick up super cheap milspec springs, and it's something really easy and non invasive that the average person can do. You just clip off little bits at a time until it's locking back. Takes like ten minutes and maybe five round of tulammo to do.

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