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Posted: 2/19/2013 7:51:43 PM EDT
| Mildength 12.5 SBR So is this a crazy suggestion or is it do able. or going to be a gas system nitemare |
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I would not go shorter than 13.5. My 14.5 midlength runs great. My rifle gas dissipator build doesn't like wolf but runs great on brass. It would probably run wolf if I opened the gas port. My carbine gas 10.0 barrel runs great on everything, I never measured the gas port on it though. It's possible if you open the gas port to around .1 or .11 it would run. It would also might be picky and only run on 5.56. ETA: 14.5 gun is using an H3 buffer, the dissy is using a rifle buffer and spring and the 10" gun is using an H or H2 buffer. (I've used both on it.) |
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I've been doing a little reading and I think you could make it work. From AR15barrels.com: From the barrel torque shoulder where the barrel extension torques against, it's 6.75" for carbine, 8.75" for mid-length and 12.125" for rifle to the step at the rear of the gas block seat. Breech face is 3/4" back from the torque shoulder. So barrel length is measured off the breech face so to get an idea of how far the port is from the muzzle we need to add .75 from the above lengths and subtract the total from the known barrel length. So the gas port on my 10" SBR is 10 - (6.75 +.75) from the muzzle, or 2.5" For my 16" dissipator its 16 - (12.125+.75) or 3.125 14.5 midlength is 5" For your planned 12.5" midlength it would be 3" This is barely shorter than my 16" dissipator but the gas port is 3.375 closer to the chamber so you will have higher pressure at the port. For estimated gas port pressure we can look at this chart.  I think it would run with a port around .09 and definitely work at .11 ETA: some good reading on gas port size http://firearmsdesigner.com/?p=234 He references a standard rifle length gas port at .099 which seems large IME. Most I have dealt with have been closer to .070 though some have been as small as .065 and others as large as .11 |
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Why not buy/build a Kino style and not worry about a potential gas system nightmare Mini Dissy (like he mentioned) would basically be a Kino with a mid length gas system. As mentioned though, I'd probably go carbine gas like the Kino for the reliability. |
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I have a 13.2" custom cut midlength SBR upper...no problems No problems with this, even with wolf? Whats the gas port size? You have me thinking....can you post pics? I finally got some pics. As I emailed you (for others to see): I don't shoot any steel case so I haven't tested that yet. I have a few rounds laying around I might be able to run through it later this spring. I don't know the gas port size. It was a 16" midlength barrel cut down by adco firearms to accommodate the shortest possible length and seat an ops inc 12th model suppressor against the fsb. it actually might be a 12.7" barrel. I think it's 13.2" with the flash hider. 
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Quoted:
Just assembled and test fired with 5 rounds of wolf in a slow fire , no changes made to port. functioned fine. and standard carbine buffer Dude, we are going to need some pics. 
Mid-length w/12.5 barrel and .070 gas port and no problems with wolf? I'm shock! |
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Quoted:
Quoted:
Just assembled and test fired with 5 rounds of wolf in a slow fire , no changes made to port. functioned fine. and standard carbine buffer Dude, we are going to need some pics.
Mid-length w/12.5 barrel and .070 gas port and no problems with wolf? I'm shock! Color me surprised! |
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Quoted: Quoted: Quoted: I have a 13.2" custom cut midlength SBR upper...no problems No problems with this, even with wolf? Whats the gas port size? You have me thinking....can you post pics? I finally got some pics. As I emailed you (for others to see): I don't shoot any steel case so I haven't tested that yet. I have a few rounds laying around I might be able to run through it later this spring. I don't know the gas port size. It was a 16" midlength barrel cut down by adco firearms to accommodate the shortest possible length and seat an ops inc 12th model suppressor against the fsb. it actually might be a 12.7" barrel. I think it's 13.2" with the flash hider. https://lh5.googleusercontent.com/-hUviqbE8dtc/UTS4v0eZTEI/AAAAAAAAFXo/yzhmJdEWWC0/s640/photo%25202.png https://lh4.googleusercontent.com/-1FaAq_OFJDM/UTS4wDUv5DI/AAAAAAAAFXw/wcwttGZTJIs/s640/photo%25203.png https://lh3.googleusercontent.com/-cvk1-a7pH7w/UTS4wsDoezI/AAAAAAAAFX4/W7Ap-4MuzGc/s640/photo%25204.png How does it sound or not sound as the case may be?
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