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Posted: 2/14/2016 12:32:09 PM EDT
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I am looking into a SBR (or Pistol) with an 11.5" barrel. I am familiar with 16" barreled carbine but not with SBRs.
Am I correct in saying that an adjustable gas block set to low (limited gas flowing back to bolt carrier) would smooth out the cycling and be less hard on the pins? I intend to use an A2 butt-stock. What would you recommend? Thanks. Note: also posted under Pistols. |
| You'll be fine no matter what you do, I'd assume. 11.5'' barrels don't usually have cycling problems that the really short barrels have had in the past. You are correct that limiting gas flow will slow the carrier speed, but difference in wear isn't really going to be noticeable. Most people prefer adjustable gas blocks when they add a suppressor to slow the greatly increased cyclic rate and reduce gas blow back. |
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Quoted:
I would combat it with springs and buffers unless you run a suppressor, then I'd look at gas block options This. I don't care for the idea of adding another mechanical component to the weapon that has a potential to fail. From what I've read 11.5 and 12.5 are pretty smooth shooters but you can tune anything to run right with proper gas port sizing, buffer weight, and springs as brad said above. |
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Quoted: This. I don't care for the idea of adding another mechanical component to the weapon that has a potential to fail. From what I've read 11.5 and 12.5 are pretty smooth shooters but you can tune anything to run right with proper gas port sizing, buffer weight, and springs as brad said above. Quoted: Quoted: I would combat it with springs and buffers unless you run a suppressor, then I'd look at gas block options This. I don't care for the idea of adding another mechanical component to the weapon that has a potential to fail. From what I've read 11.5 and 12.5 are pretty smooth shooters but you can tune anything to run right with proper gas port sizing, buffer weight, and springs as brad said above. I would agree with that for 'most' cases. However, if you just Google 'Colt gas port sizes' you see bad info floating out there for years saying a 10.5 should be .093". That is way too large. Consider NSWC Crane specs out .070 for the 10.3" MK18. Springs and buffers can only do so much when the port is that huge. Not to mention that springs/buffers don't reduce the excess fouling coming into the action when excessively overgassed. Regarding concern of a mechanical component failing... Our 'baby Govnah' is just a regular low profile gas block that has been countersunk to allow for some mis-alignment and the port is drilled to .043". So in this example, you could just drill it out to .070" (for running milspec ammo and buffer/spring) or have us do it and you have one solid piece of steel. There are no moving parts. I think this would be a better solution than resorting to special springs/buffers. It is also only $30 which is probably less you'll spend on a special spring and buffer. Especially if you have one SBR and multiple uppers. It is easier to have each upper tuned and have your lower in a standard 'milspec' configuration so you just swap uppers and don't play musical buffers/springs every time you change uppers.  |
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Quoted: I would agree with that for 'most' cases. However, if you just Google 'Colt gas port sizes' you see bad info floating out there for years saying a 10.5 should be .093". That is way too large. Consider NSWC Crane specs out .070 for the 10.3" MK18. Springs and buffers can only do so much when the port is that huge. Not to mention that springs/buffers don't reduce the excess fouling coming into the action when excessively overgassed. Regarding concern of a mechanical component failing... Our 'baby Govnah' is just a regular low profile gas block that has been countersunk to allow for some mis-alignment and the port is drilled to .043". So in this example, you could just drill it out to .070" (for running milspec ammo and buffer/spring) or have us do it and you have one solid piece of steel. There are no moving parts. I think this would be a better solution than resorting to special springs/buffers. It is also only $30 which is probably less you'll spend on a special spring and buffer. Especially if you have one SBR and multiple uppers. It is easier to have each upper tuned and have your lower in a standard 'milspec' configuration so you just swap uppers and don't play musical buffers/springs every time you change uppers. http://cdn3.bigcommerce.com/s-j1m3pz/products/139/images/411/babygovnah3_1024x768__02192.1421685106.1280.1280.jpg?c=2 Quoted: Quoted: Quoted: I would combat it with springs and buffers unless you run a suppressor, then I'd look at gas block options This. I don't care for the idea of adding another mechanical component to the weapon that has a potential to fail. From what I've read 11.5 and 12.5 are pretty smooth shooters but you can tune anything to run right with proper gas port sizing, buffer weight, and springs as brad said above. I would agree with that for 'most' cases. However, if you just Google 'Colt gas port sizes' you see bad info floating out there for years saying a 10.5 should be .093". That is way too large. Consider NSWC Crane specs out .070 for the 10.3" MK18. Springs and buffers can only do so much when the port is that huge. Not to mention that springs/buffers don't reduce the excess fouling coming into the action when excessively overgassed. Regarding concern of a mechanical component failing... Our 'baby Govnah' is just a regular low profile gas block that has been countersunk to allow for some mis-alignment and the port is drilled to .043". So in this example, you could just drill it out to .070" (for running milspec ammo and buffer/spring) or have us do it and you have one solid piece of steel. There are no moving parts. I think this would be a better solution than resorting to special springs/buffers. It is also only $30 which is probably less you'll spend on a special spring and buffer. Especially if you have one SBR and multiple uppers. It is easier to have each upper tuned and have your lower in a standard 'milspec' configuration so you just swap uppers and don't play musical buffers/springs every time you change uppers. http://cdn3.bigcommerce.com/s-j1m3pz/products/139/images/411/babygovnah3_1024x768__02192.1421685106.1280.1280.jpg?c=2 |
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Quoted: What is the ideal gas port size for 11.5" barrel? In a perfect world, all barrels would be ported the same. 20 years ago, you didn't have Walmarts selling imported steel cased ammo which is using the same powder in their 7.62x39mm ammo offerings which is faster burning. This is discussed well here: http://www.luckygunner.com/labs/brass-vs-steel-cased-ammo/  As seen in the chart above port pressure is low for Tula in comparison to other rounds. So if your gun runs Tula it will be overgassed when running Milspec ammo. This is also discussed here: http://www.recoilweb.com/micromoas-govnah-adjustable-gas-block-38489.html In the Recoil article, it was a BCM 11.5" barrel used and ported from the factory at .073 which would run anything. .063 ran milspec ammo fine. Chart below is taken from part 2 of the Recoil article: http://www.recoilweb.com/micromoas-govnah-adjustable-gas-block-pt-2-of-2-38639.html  So to answer you question, 'ideal' port size is not a simple answer and is subjective. We port our 11.5" barrels at .063" which is probably one of the smallest if not the smallest you'll find in the industry....which is for OUR barrels and may not work for your barrel based on the reasons mentioned above in the first link. When purchased with a Govnah, we port the barrel to .073" with a 3 position regulator plate ported to: .063/.049/.073 for optimal unsuppressed/suppressed/adverse If you want it to run 'anything' then go with .073". If you want it to run only milspec pressure ammo then go .063" also accepting the fact that if it gets too fouled it may not run. Note that is OUR barrels and may not work for other bores/chambers as discussed in the first link I posted above. This is also assuming you are running a standard power buffer spring and no heavier than an H2 buffer and also assuming your barrel was NOT chambered too loose or tight on the tolerances and your bore diameter isn't loose or your talking about a shot out bore. |
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Quoted:
I would agree with that for 'most' cases. However, if you just Google 'Colt gas port sizes' you see bad info floating out there for years saying a 10.5 should be .093". That is way too large. Consider NSWC Crane specs out .070 for the 10.3" MK18. Springs and buffers can only do so much when the port is that huge. Not to mention that springs/buffers don't reduce the excess fouling coming into the action when excessively overgassed. Regarding concern of a mechanical component failing... Our 'baby Govnah' is just a regular low profile gas block that has been countersunk to allow for some mis-alignment and the port is drilled to .043". So in this example, you could just drill it out to .070" (for running milspec ammo and buffer/spring) or have us do it and you have one solid piece of steel. There are no moving parts. I think this would be a better solution than resorting to special springs/buffers. It is also only $30 which is probably less you'll spend on a special spring and buffer. Especially if you have one SBR and multiple uppers. It is easier to have each upper tuned and have your lower in a standard 'milspec' configuration so you just swap uppers and don't play musical buffers/springs every time you change uppers. http://cdn3.bigcommerce.com/s-j1m3pz/products/139/images/411/babygovnah3_1024x768__02192.1421685106.1280.1280.jpg?c=2 Quoted:
Quoted:
Quoted:
I would combat it with springs and buffers unless you run a suppressor, then I'd look at gas block options This. I don't care for the idea of adding another mechanical component to the weapon that has a potential to fail. From what I've read 11.5 and 12.5 are pretty smooth shooters but you can tune anything to run right with proper gas port sizing, buffer weight, and springs as brad said above. I would agree with that for 'most' cases. However, if you just Google 'Colt gas port sizes' you see bad info floating out there for years saying a 10.5 should be .093". That is way too large. Consider NSWC Crane specs out .070 for the 10.3" MK18. Springs and buffers can only do so much when the port is that huge. Not to mention that springs/buffers don't reduce the excess fouling coming into the action when excessively overgassed. Regarding concern of a mechanical component failing... Our 'baby Govnah' is just a regular low profile gas block that has been countersunk to allow for some mis-alignment and the port is drilled to .043". So in this example, you could just drill it out to .070" (for running milspec ammo and buffer/spring) or have us do it and you have one solid piece of steel. There are no moving parts. I think this would be a better solution than resorting to special springs/buffers. It is also only $30 which is probably less you'll spend on a special spring and buffer. Especially if you have one SBR and multiple uppers. It is easier to have each upper tuned and have your lower in a standard 'milspec' configuration so you just swap uppers and don't play musical buffers/springs every time you change uppers. http://cdn3.bigcommerce.com/s-j1m3pz/products/139/images/411/babygovnah3_1024x768__02192.1421685106.1280.1280.jpg?c=2 I actually like that, but I'll ask the question you probably know I'm going to ask: Do you see any accelerated erosion in either the gas block or port due to that bottleneck and gas expansion in the countersunk "pocket"? Might have to try one... 
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Quoted: I actually like that, but I'll ask the question you probably know I'm going to ask: Do you see any accelerated erosion in either the gas block or port due to that bottleneck and gas expansion in the countersunk "pocket"? Might have to try one... Quoted: Quoted: Quoted: Quoted: I would combat it with springs and buffers unless you run a suppressor, then I'd look at gas block options This. I don't care for the idea of adding another mechanical component to the weapon that has a potential to fail. From what I've read 11.5 and 12.5 are pretty smooth shooters but you can tune anything to run right with proper gas port sizing, buffer weight, and springs as brad said above. I would agree with that for 'most' cases. However, if you just Google 'Colt gas port sizes' you see bad info floating out there for years saying a 10.5 should be .093". That is way too large. Consider NSWC Crane specs out .070 for the 10.3" MK18. Springs and buffers can only do so much when the port is that huge. Not to mention that springs/buffers don't reduce the excess fouling coming into the action when excessively overgassed. Regarding concern of a mechanical component failing... Our 'baby Govnah' is just a regular low profile gas block that has been countersunk to allow for some mis-alignment and the port is drilled to .043". So in this example, you could just drill it out to .070" (for running milspec ammo and buffer/spring) or have us do it and you have one solid piece of steel. There are no moving parts. I think this would be a better solution than resorting to special springs/buffers. It is also only $30 which is probably less you'll spend on a special spring and buffer. Especially if you have one SBR and multiple uppers. It is easier to have each upper tuned and have your lower in a standard 'milspec' configuration so you just swap uppers and don't play musical buffers/springs every time you change uppers. http://cdn3.bigcommerce.com/s-j1m3pz/products/139/images/411/babygovnah3_1024x768__02192.1421685106.1280.1280.jpg?c=2 I actually like that, but I'll ask the question you probably know I'm going to ask: Do you see any accelerated erosion in either the gas block or port due to that bottleneck and gas expansion in the countersunk "pocket"? Might have to try one... On top of that you have no point of reference with that method and have no idea what the port size is. On a numbered bit set, the next bit size up from .070 is .073. If you can stick the shank of a .073 bit in there, maybe you should change it. If you have read through the 'Battlefield Vegas Thread' those guys run more rounds than most anyone on here has on their full auto rental range. They are running baby Govnah's on their full auto rental PDW's with 7.5" barrels. You are talking about 30K psi with pistol length gas. See it mentioned on this thread: http://www.ar15.com/forums/t_3_118/677135_High_round_count_AR_M4_s__over_100_000_rounds__and_how_they_have_handled_on_our_range.html&page=21 You can also see how we tested our regular our Govnah here: http://micromoa.com/ak74-test-barrel/ Gas port in the test barrel was severly eroded but the reguator plate still in spec since it is port based as discussed vs pinching off the gas with a set screw.  |
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Quoted: Thank you very much Amphibian! The 11.5" barrels (Aero Precision) I bought have 0.073" holes. I am still considering though an adjustable gas block. Does the fact of using an A2 make much difference as compared to a collapsable carbine stock? You can see what results we got with our 16"/17.3" Rifle gas setups: http://micromoa.com/16-17.3-rifle-gas-competition-setup/ Port sizes about the same when using carbine (stock carbine buffer) or A2. |
| I love my 3 position Govnah. Shot ~1500 rounds between changing settings on the Govnah and it was as easy to adjust as the day I bought it. That is on a Rainer barrel. My next build will be a 300 BLK SBR and I plan to run a Micro MOA barrel and Govnah on it...when they are released. |
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