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Thread: Colt with 11.5" barrel failing to lock back on last round

  1. #41
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    Crane spec is .071. .072 is in no way "severely" overgassed for an 11.5".

    Quote Originally Posted by TinyCrumb View Post
    I'm not meaning to step on anyone's toes here, but I disagree with a lot of the information in this thread.

    The gas on an 11.5 should be smaller than a 10.3, not larger. .070 is Crane spec for 5.56 Nato out of 10.3" barrels. .063 is stock 14.5" Colt Carbine. The 11.5 has more dwell time than the 10.3 and less than the 14.5".

    If the barrel had been chopped to 10.3" with no gas port work, you would have seen more drastic short stroking. Since you only cut to 11.5, you didn't reduce the dwell time as drastic as 10.3" would have, but enough that your rifle was functioning *just* on the verge of reliability (i.e., rifle would cycle but would not lock back on last round).

    My opinion is you went about this all wrong. First off, I would have got the correct gas port spec. Secondly, I would be tuning the rifle for a carbine or H buffer, not *starting* with an H3.

    Something around .067/.068 would have given you a properly gassed rifle with a carbine or H buffer.

    You now have a severely overgassed rifle, and even though you're able to use an H3 to tame it down, you're at the end of your buffer options already and you'll experience faster port erosion and parts wear than necessary.

    ----------

    The 10.3" barrel ends pretty quickly right after the gas port, which means the system only stays pressurized for a very short amount of time. Because of this, the gas port needs to be "enlarged" to insure there's still enough pressure in that short amount of time to cycle the action. The longer you increase the barrel after the gas port, the longer the system remains under pressure and the smaller port is proper for proper functioning. A 14.5"/16" factory Colt for instance will have a port of around .063 from the factory.

    I really don't understand the advice in here saying an 11.5" should have a larger port than 10.3".



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  2. #42
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    There's combinations that are worse for sure. With a normal 5.56 chamber, throat, and bore, with 5.56 port pressure ammo, does an 11.5" carbine gas gas 5.56 AR require that port size? Maybe a better question to ask is what port sizes are preferable to those applications?

  3. #43
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    Quote Originally Posted by TinyCrumb View Post
    I'm not meaning to step on anyone's toes here, but I disagree with a lot of the information in this thread.

    The gas on an 11.5 should be smaller than a 10.3, not larger. .070 is Crane spec for 5.56 Nato out of 10.3" barrels. .063 is stock 14.5" Colt Carbine. The 11.5 has more dwell time than the 10.3 and less than the 14.5".

    If the barrel had been chopped to 10.3" with no gas port work, you would have seen more drastic short stroking. Since you only cut to 11.5, you didn't reduce the dwell time as drastic as 10.3" would have, but enough that your rifle was functioning *just* on the verge of reliability (i.e., rifle would cycle but would not lock back on last round).

    My opinion is you went about this all wrong. First off, I would have got the correct gas port spec. Secondly, I would be tuning the rifle for a carbine or H buffer, not *starting* with an H3.

    Something around .067/.068 would have given you a properly gassed rifle with a carbine or H buffer.

    You now have a severely overgassed rifle, and even though you're able to use an H3 to tame it down, you're at the end of your buffer options already and you'll experience faster port erosion and parts wear than necessary.

    ----------

    The 10.3" barrel ends pretty quickly right after the gas port, which means the system only stays pressurized for a very short amount of time. Because of this, the gas port needs to be "enlarged" to insure there's still enough pressure in that short amount of time to cycle the action. The longer you increase the barrel after the gas port, the longer the system remains under pressure and the smaller port is proper for proper functioning. A 14.5"/16" factory Colt for instance will have a port of around .063 from the factory.

    I really don't understand the advice in here saying an 11.5" should have a larger port than 10.3".
    Even though I'm the one who has been asking questions here, your post is simply incorrect. The Crane spec .071" is designed for 5.56 only, and with a suppressor. That's why it's small. Most companies seem to use .080-.093" for 10.3" barrels to allow them to fire lower pressure .223 ammo, and without a suppressor.
    The same goes with my 11.5" rifle; my primary ammunition will be .223, and most often without a suppressor.
    So I am perfectly comfortable with my .072" port on 11.5" barrel, which is smaller than most companies (BCM of .076", Colt of .080") but large enough for reliability.
    Last edited by masakari; 12-30-15 at 12:58.

  4. #44
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    I could argue on who's post is incorrect or more preferably applied, least correct.
    Maybe a question could be posed as to what the gas porting ranges offer? In terms of operation, and how those possibilities could conflict in that.

  5. #45
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    Quote Originally Posted by masakari View Post
    Even though I'm the one who has been asking questions here, your post is simply incorrect. The Crane spec .071" is designed for 5.56 only, and with a suppressor. That's why it's small. Most companies seem to use .080-.093" for 10.3" barrels to allow them to fire lower pressure .223 ammo, and without a suppressor.
    The same goes with my 11.5" rifle; my primary ammunition will be .223, and most often without a suppressor.
    So I am perfectly comfortable with my .072" port on 11.5" barrel, which is smaller than most companies (BCM of .076", Colt of .080") but large enough for reliability.
    Um, no.

    1. The Crane spec is .070 (not .071) AND it's for 10.3" barrels, not 11.5" barrels (very different). Secondly, the spec is not "with a suppressor". The spec is to run standard 5.56 M855 unsuppressed with maximum reliability and minimal parts wear and port erosion.

    2. "Most" companies do not use .080 - .093 in their 10.3" barrels, there's only one company that uses something even close to that and it's DD in their 10.3" barrel. Yes, they do it for reliability, but you'll be hard pressed to find a person who doesn't think they go to far and their 10.3" rifles are notoriously overgassed. All other 10.~ barrel manufacturers (Colt, LMT, Noveske, BA, etc…) use a port of around .074 - .078. And all of those barrels function just fine with an H buffer and lower power .223 (include steel cased).

    3. Your "11.5" rifle is a totally different animal than a 10.3" rifle and comparing the gas port sizes to it is simply wrong. You have more dwell time with the 11.5" barrel. The pressure remains for a longer period of time, meaning you need less gas than a 10.3" would.

    4. It doesn't really matter what you're comfortable with. If your rifle shoots lower power .223 with an H3 buffer unsuppressed and functions fine and locks back on the last round … then …you're overgassed. Will it be reliable? Maybe.
    Last edited by TinyCrumb; 12-30-15 at 18:37.

  6. #46
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    If you have ever worked with Crane, you could know about the issues that deal with them.
    10"ish 5.56 ARs may be called a different animal, but other species then share traits. The 11.5" 5.56 is aligned with those traits. A .070" ported 10"ish doesn't require the can to function with M855.
    The DD example is over gassed. Unfortunately, many others are over gas as well. That gassing approach may help some with a larger detriment to others.
    Remember, that the term "dwell" as referred to gas drive is really just an amount of energy in time that can operate the system combined with the porting. Porting is the physical supply size, dwell is the quantity of the timing of that. The required volume is the amount of those in conjunction. Insufficient energy into the system results in issues, excess energy into the system results in issues. The balance of the amount needed for a wide or wider span of operation falls between.

  7. #47
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    I got a 10.5" barrel from Odin Works with .083" gas port and it was grossly over gassed. An H2 buffer slowed things down enough to make it shootable, but it took an adjustable gas block to get it running smoothly
    Last edited by MistWolf; 12-31-15 at 12:07.
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  8. #48
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    Maybe another question to pose is, how much work can be required to operate the system? What variables could be involved?

  9. #49
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    LMT used to use a .071 port as well and recently switched to .078 for commercial stuff. Noveske uses a .081 port. Measured multiple times on multiple barrels with pin gages. I have measured 3 different Rainier Arms barrels and all were at .071-.072. Those barrels worked fine unsuppressed with M855 and M193.

    Quote Originally Posted by TinyCrumb View Post
    Um, no.

    1. The Crane spec is .070 (not .071) AND it's for 10.3" barrels, not 11.5" barrels (very different). Secondly, the spec is not "with a suppressor". The spec is to run standard 5.56 M855 unsuppressed with maximum reliability and minimal parts wear and port erosion.

    2. "Most" companies do not use .080 - .093 in their 10.3" barrels, there's only one company that uses something even close to that and it's DD in their 10.3" barrel. Yes, they do it for reliability, but you'll be hard pressed to find a person who doesn't think they go to far and their 10.3" rifles are notoriously overgassed. All other 10.~ barrel manufacturers (Colt, LMT, Noveske, BA, etc…) use a port of around .074 - .078. And all of those barrels function just fine with an H buffer and lower power .223 (include steel cased).

    3. Your "11.5" rifle is a totally different animal than a 10.3" rifle and comparing the gas port sizes to it is simply wrong. You have more dwell time with the 11.5" barrel. The pressure remains for a longer period of time, meaning you need less gas than a 10.3" would.

    4. It doesn't really matter what you're comfortable with. If your rifle shoots lower power .223 with an H3 buffer unsuppressed and functions fine and locks back on the last round … then …you're overgassed. Will it be reliable? Maybe.



    Owner/Instructor at Semper Paratus Arms

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  10. #50
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    With a normal chamber, throat, and bore. What porting could be more desirable with 5.56 ammo? Catering to a lower port pressure ammunition offering may not lead to a wider span of function overall. A porting that has the possibility of options is preferable to one without in my opinion. I would tend to prefer a porting that supports a H2 carbine action for most, more mass may be added with a can, less mass can be used without a can and lower port pressure ammo. When a porting drives you to the end of either spectrum, your options are reduced.

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