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Posted: 3/7/2022 6:20:04 PM EDT
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Just trying to get a handle on what the appropriate GP size should be for a given barrel length in order to compare it to what manufacturers are currently putting out. I'm just trying to establish what the base line should be, so I chose Colt's GP diameters as the base line. I'm just trying to determine how over-gassed, or not, a barrel is by having something to compare it to. Big thanks to @Molon, as I am able to obtain GP size information from his posts. Colt's gas port sizes are: 10.3" - .070" (The NSW Crane spec for the 10.3" Mk18 barrels is 0.070") 11.5" - .070" FBI/HRT SOCOM 11.5" - .074" Colt 6933/Commando 14.5" - .062" (carbine gas) 16" - .062" (carbine gas) 16" - 0.071 (6960 mid-length) DD GP sizes: 10.3” - .070" 11.5” - .069" 14.5 - .076" 16” - .073 (mid-length) (Big thanks to everyone helping me with the above info!) What would be the most appropriate GP size for: 1) 14.5" mid-length 2) 16" mid-length Some information gleaned from Molon's posts: BRT 16" Pro barrel: mid-length, GP 0.073” (Thanks to Molon for providing the GP info - Stay tuned for his pending review). Criterion Core 16" barrel: mid-length, GP 0.078". Geissele 16" CHF barrel: mid-length, GP 0.062”. Hodge Defense 14.5" barrel: mid-length, GP 0.075”. Noveske N4 Light 16" barrel: mid-length , GP info not posted. TRIARC 16" Track 2.0 barrel: mid-length, GP 0.0695". =========================================================================================================================================== I came across this spreadsheet doing a search, but have no idea as to its accuracy: GP data sheet, unknown origin I found the following in the above link: Noveske N4 16 Midlength 0.081 Self-measured 8/16/2017 Noveske N4 16 Midlength 0.083 Self-measured 8/1/2018 Noveske N4 14.5 Midlength 0.081 Self-measured 9/1/2013 Pin Gauge Measured And here is another GP size resource. |
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Aero Precision list most of their gas port sizes for both 5.56 and 223 Wylde barrels. AERO 5.56 NATO Aero .223 Wylde Summary: 5.56 & 223 Wylde Carbine Length are mostly 0.0635 Mid Length are mostly 0.0785 Rifle Length are mostly 0.0935 A few they do not list at all and a few do not fit the above "mostly" category and have mid length gas port sizes with short carbine gas barrels..... |
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Quoted: Thank you, Tig. @TGWLDR @SAMUSE Any thoughts on what the best GP size would be for these lengths? 1) 14.5" mid-length 2) 16" mid-length Quoted: Quoted: Colt GP diameters listed in OP at .063" should be .062" Thank you, Tig. @TGWLDR @SAMUSE Any thoughts on what the best GP size would be for these lengths? 1) 14.5" mid-length 2) 16" mid-length .073” .071” |
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Quoted: .073” .071” Quoted: Quoted: Quoted: Colt GP diameters listed in OP at .063" should be .062" Thank you, Tig. @TGWLDR @SAMUSE Any thoughts on what the best GP size would be for these lengths? 1) 14.5" mid-length 2) 16" mid-length .073” .071” Colt 6960 is .071" , IIRC. .072-.073" for 14.5" is probably right in the sweet spot. No expert though. |
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Quoted: Colt 6960 is .071" , IIRC. .072-.073" for 14.5" is probably right in the sweet spot. No expert though. Quoted: Quoted: Quoted: Quoted: Colt GP diameters listed in OP at .063" should be .062" Thank you, Tig. @TGWLDR @SAMUSE Any thoughts on what the best GP size would be for these lengths? 1) 14.5" mid-length 2) 16" mid-length .073” .071” Colt 6960 is .071" , IIRC. .072-.073" for 14.5" is probably right in the sweet spot. No expert though. I completely forgot about the Colt middy 6960 |
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There’s no real consensus on what’s “best” — some manufacturers have them on the larger side to ensure reliable operation even with mild ammo, some on the smaller side to keep them soft shooting. You can get an idea of the range of what’s out there from these sites: https://docs.google.com/spreadsheets/d/1tXunBDX5Gaz87BqxwNxDUlWNK9nEv-cZEQoLq2JXXrk/htmlview https://sites.google.com/view/black-rifle-haven/gas-port-reference-charts |
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Quoted: There’s no real consensus on what’s “best” — some manufacturers have them on the larger side to ensure reliable operation even with mild ammo, some on the smaller side to keep them soft shooting. You can get an idea of the range of what’s out there from these sites: https://docs.google.com/spreadsheets/d/1tXunBDX5Gaz87BqxwNxDUlWNK9nEv-cZEQoLq2JXXrk/htmlview https://sites.google.com/view/black-rifle-haven/gas-port-reference-charts I would really prefer to have a properly gassed barrel, as I primarily shoot XM193 for practice. I know that manufacturers tend to go bigger so people don't complain about their barrels not cycling shitty ammo, but I do think there is a "sweet spot" for a given barrel length and GP size. Plus, an over-gassed system will beat up the rifle more, no? But, I know that most people don't shoot their rifles enough to ever notice. At any rate, I just like knowing what the correct spec is for things. |
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I measured a few gas ports, this is what I came up with. Colt 10.3” = .0685 (Prod. Date) 07/19 Colt 6933 11.5” = .074 (Prod. Date) 02/20 Colt FBI/HRT = .069 (Prod. Date) 08/15 Colt 14.5” = .0615 (Prod. Date) 04/09 Colt 16” mid = .071 (Prod. Date) 03/17 Hodge Defense 14.5” = .074 (Prod. Date) 09/19 Noveske 14.5” = .080 (Prod. Date) 11/19 DD stated port sizes 16” mid = .073 14.5 =.076 11.5” = .069 10.3” =.070 I think .074 is perfect for a 14.5 mid. My Hodge Defense barrel ejects M193 between 4:00-4:30 with a Colt H2 buffer and spring, haven’t tried with an H buffer. |
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Quoted: I measured a few gas ports, this is what I came up with. Colt 10.3” = .0685 (Prod. Date) 04/20 Colt 6933 11.5” = .074 (Prod. Date) 02/20 Colt FBI/HRT = .069 (Prod. Date) 08/15 Colt 14.5” = .0615 (Prod. Date) 04/09 Colt 16” mid = .071 (Prod. Date) 03/17 Hodge Defense 14.5” = .074 (Prod. Date) 09/19 Noveske 14.5” = .080 (Prod. Date) 11/19 DD stated port sizes 16” mid = .073 14.5 =.076 11.5” = .069 10.3” =.070 I think .074 is perfect for a 14.5 mid. My Hodge Defense barrel ejects M193 between 4:00-4:30 with a Colt H2 buffer and spring, haven’t tried with an H buffer. @FONTY : Much thanks for the above information. It's interesting to see how large Noveske GPs are. |
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Quoted: Glad to help, i purchased a BRT .076 gas tube which equals a .074 gas port for Noveske’s ridiculously huge gas port. Quoted: Quoted: @FONTY : Much thanks for the above information. It's interesting to see how large Noveske GPs are. Glad to help, i purchased a BRT .076 gas tube which equals a .074 gas port for Noveske’s ridiculously huge gas port. I have a Noveske 16” N4 upper, so I will definitely look into that. Thanks! @FONTY: Is your Noveske a 14.5" or 16" N4 barrel? |
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Quoted: I measured a few gas ports, this is what I came up with. Colt 10.3” = .0685 (Prod. Date) 04/20 Colt 6933 11.5” = .074 (Prod. Date) 02/20 Colt FBI/HRT = .069 (Prod. Date) 08/15 Colt 14.5” = .0615 (Prod. Date) 04/09 Colt 16” mid = .071 (Prod. Date) 03/17 Hodge Defense 14.5” = .074 (Prod. Date) 09/19 Noveske 14.5” = .080 (Prod. Date) 11/19 DD stated port sizes 16” mid = .073 14.5 =.076 11.5” = .069 10.3” =.070 I think .074 is perfect for a 14.5 mid. My Hodge Defense barrel ejects M193 between 4:00-4:30 with a Colt H2 buffer and spring, haven’t tried with an H buffer. Thanks FONTY. Always solid info. More variance than I thought in barrels. |
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Quoted: 14.5" middy - .073" 16" middy - .071" Got it. Thanks! ETA: If the GP numbers that I found for the Noveske N4 are correct, those barrels are pretty over-gassed. Interesting. Quoted: Quoted: .073” .071” 14.5" middy - .073" 16" middy - .071" Got it. Thanks! ETA: If the GP numbers that I found for the Noveske N4 are correct, those barrels are pretty over-gassed. Interesting. Yep. They big. I forgot to mention that I don’t shoot .223 at all. Everything I shoot is decent or better quality 5.56. If you have specific ammo in mind a bigger port can help. |
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There are also other factors that I don’t understand but must also effect performance. I have two 14.5” mid-lengths, both with the same port size but they perform differently. And this is not just my “feelings”. I put the same size BRT gas restricting tube in them and one of them fails to lock back a carbine buffer in cold weather whereas the other one has not problem locking back an H2 with the same ammo on the same day. So maybe exacting specifications of the bore size? Different kind of rifling? Something is causing a performance difference between them. The comparatively “overpassed” barrel is a criterion and the “undergassed” one is a Rosco. Both 0.750 at the gas block. The criterion has always felt overgassed but with its 0.078 gas port is about where everyone says it should be for a 14.5” mid. Edit to correct gas port size |
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Quoted: There are also other factors that I don’t understand but must also effect performance. I have two 14.5” mid-lengths, both with the same port size but they perform differently. And this is not just my “feelings”. I put the same size BRT gas restricting tube in them and one of them fails to lock back a carbine buffer in cold weather whereas the other one has not problem locking back an H2 with the same ammo on the same day. So maybe exacting specifications of the bore size? Different kind of rifling? Something is causing a performance difference between them. The comparatively “overpassed” barrel is a criterion and the “undergassed” one is a Rosco. Both 0.750 at the gas block. The criterion has always felt overgassed but with its 0.074 gas port is about where everyone says it should be for a 14.5” mid. Is your Criterion barrel one of the Core Series barrels? As for the Rosco barrel, I only see Bloodline barrels with a gov profile. That is an interesting difference. Did you personally gauge the GP yourself? Plus, what were the GP sizes for your barrels? By the way, I found this on the Criterion website: 0.625” Gas Block journal, dimpled for ease of installation and solid lock-up |
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Quoted: Some information gleaned from Molon's posts: Noveske N4 Light 16" barrel: mid-length , |
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Quoted: @Molon: Do you happen to have the GP size for this barrel? It appears that the numbers I have posted based on what I found on "da internets" is wrong, correct? I also deleted that info from the OP, as that was probably giving the impression that those numbers were coming from you, which they did not. |
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Quoted: @Molon: Do you happen to have the GP size for this barrel? It appears that the numbers I have posted based on what I found on "da internets" is wrong, correct? Your numbers are probably right for todays productions, but the Noveske barrels that I owned didn't have the large gas ports that they seem to have today. I don't recall the exact diameter of the gas port on the 16" N4, but IIRC the diameter of the gas port on my 16" Noveske RECON barrels (with mid-length gas system) was 0.072". ... |
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Quoted: Your numbers are probably right for todays productions, but the Noveske barrels that I owned didn't have the large gas ports that they seem to have today. I don't recall the exact diameter of the gas port on the 16" N4, but IIRC the diameter of the gas port on my 16" Noveske RECON barrels (with mid-length gas system) was 0.072". ... Thanks for the response and the additional data point. Do you happen to remember if you purchased that RECON barrel while John was alive? It seems like a lot of people appear to have the opinion that some things changed in the years after John's passing. |
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Quoted: Is your Criterion barrel one of the Core Series barrels? As for the Rosco barrel, I only see Bloodline barrels with a gov profile. That is an interesting difference. Did you personally gauge the GP yourself? Plus, what were the GP sizes for your barrels? By the way, I found this on the Criterion website: 0.625” Gas Block journal, dimpled for ease of installation and solid lock-up Criterion barrel is the hybrid series. Not sure if they still make those. Rosco barrel is the bloodline gov”t mid length. I did measure them myself. I have a set of numbered bits. The 0.076 fit with some slop but the 0.0785 did not fit. Both of them seemed to have the same amount of slop. It is possible that one is 0.077 and one is 0.078 but I think they are both the same. Gas block size is .750 for both. |
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Quoted: Criterion barrel is the hybrid series. Not sure if they still make those. Rosco barrel is the bloodline gov”t mid length. I did measure them myself. I have a set of numbered bits. The 0.076 fit with some slop but the 0.0785 did not fit. Both of them seemed to have the same amount of slop. It is possible that one is 0.077 and one is 0.078 but I think they are both the same. Gas block size is .750 for both. Ah, okay, so it's a Hybrid barrel. I just looked it up, and, yup, gas block size for that barrel is .750. The gas block size I included in my post above was for the Core Series barrel, which is 0.625." |
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Centurion Arms seems to have settled on more middle of the road gas port sizing for their current production: Midlength - Lightweight CHF 16in .076 13.7in .075 Midlength - Medium CHF 16in .075" 14.5" .075" My main rifle is the 13.7" LW and it feels very well gassed but admittedly I have not tried it with a suppressor. Functions perfectly with all of the ammo I've shot out of it, all brass mostly PMC |
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Quoted: Centurion Arms seems to have settled on more middle of the road gas port sizing for their current production: Midlength - Lightweight CHF 16in .076 13.7in .075 Midlength - Medium CHF 16in .075" 14.5" .075" My main rifle is the 13.7" LW and it feels very well gassed but admittedly I have not tried it with a suppressor. Functions perfectly with all of the ammo I've shot out of it, all brass mostly PMC @msch42: Did you pin gauge these yourself? Where did you get the numbers from? |
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Quoted: @urbankaos04 They have their current production gas port sizes on their website for all of their CHF offerings, they don't on their Recce/MK12 stainless though Well, that is mighty nice of them considering everyone else is so secretive. Thanks for the heads up. |
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Will be updating the OP with this new juicy tidbit. Geissele 16” CHF Barrel: Attached File |
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I measured the gas port on my Noveske N4 16" mid-length today at 0.078" with a set of pin gauges. I've had this barrel for ages, and it's been languishing since I pulled it off my KAC URX III build. IIRC, at the time I got it, Noveske was saying it was tuned for use with an H2 buffer. My opinion is it's over gassed, especially if you intend to use a silencer, but man I lover the profile Noveske used. I've also got a CHF CL barrel from Centurion that started out as a 14.5" with a standard front sight base. It's a carbine-length gas system and is govt. profile behind the front sight and a narrower contour forward to the muzzle. The gas port gauged at 0.069" so I cut it down to 11.5" and it's been great with or without a can. |
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I’ve been working on a Noveske bbl 14.5 mid gas build. I’m thinking with the large GP it will run smooth as silk on an A5, LMT E carrier, and K size suppressor. My thought is that setup will supply adequate gas for light loads, but the carrier/buffer will negate/tame excessive gas with full house loads. Who knows, maybe it will be a turd. |
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Quoted: I’ve been working on a Noveske bbl 14.5 mid gas build. I’m thinking with the large GP it will run smooth as silk on an A5, LMT E carrier, and K size suppressor. My thought is that setup will supply adequate gas for light loads, but the carrier/buffer will negate/tame excessive gas with full house loads. Who knows, maybe it will be a turd. Definitely NOT. They might be a little over gassed for SOME applications, but they're excellent shooting barrels. |
| I have 14.5” Spikes midlength (non CHF), that felt a tad overgassed. Installed a BRT .076” tube which mimics a ~.073” gas port. Rifle is very soft now, could have probably gone smaller to a .073” BRT gas tube. No problem with full power or cheap Tula locking a FA BCG and H2 back. |
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Quoted: I have 14.5” Spikes midlength (non CHF), that felt a tad overgassed. Installed a BRT .076” tube which mimics a ~.073” gas port. Rifle is very soft now, could have probably gone smaller to a .073” BRT gas tube. No problem with full power or cheap Tula locking a FA BCG and H2 back. Nice to know that these BRT tubes do the trick. |
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Quoted: Definitely NOT. They might be a little over gassed for SOME applications, but they're excellent shooting barrels. I agree that they are great shooting barrels (I have a 16" N4 Light upper), but having a .081 GP unnecessarily over-gasses the rifle and just batters the rifle more. Of course, some people may not care. It would just be nice to have a properly gassed rifle, no more, no less. |
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Quoted: I agree that they are great shooting barrels (I have a 16" N4 Light upper), but having a .081 GP unnecessarily over-gasses the rifle and just batters the rifle more than it has to be. Of course, some people may not care. It would just be nice to have a properly gassed rifle, no more, no less. Agree completely, and 0.081" is definitely pushing it. It does amaze me Noveske went that big on them. I really liked their carbine gas N4s as well, but also way over gassed. |
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Quoted: @urbankaos04 They have their current production gas port sizes on their website for all of their CHF offerings, they don't on their Recce/MK12 stainless though I finally took the time to look up DD GP sizes, but could not find the info. They give the gas block journal size, but not the GP diameter size: Gas SystemMid-length Diameter At Gas Port.750? @msch42 That is the diameter for gas block journal size and it is the same across all of their barrels. Or maybe I'm not looking hard enough? 
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Quoted: DD stated port sizes 16” mid = .073 14.5 =.076 11.5” = .069 10.3” =.070 I think .074 is perfect for a 14.5 mid. My Hodge Defense barrel ejects M193 between 4:00-4:30 with a Colt H2 buffer and spring, haven’t tried with an H buffer. @Fonty: I take it that for the DD 14.5" barrel listed above is for a mid-length?? |
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