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Old 10-27-2012, 8:56 AM
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Intimid8tor Intimid8tor is offline
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Default Gas vents in upper

I'm throwing around some ideas here as I am waiting for my tax stamps to be able to build 2 SBR with suppressors. One will be in 9mm and one will be either .223 or .300blk.

One of the common challenges is that the increased pressure blows gas back into the face of the shooter. I use right handed rifles, but shoot left handed.

I know about the forward assist gas vents and PRI gas buster. They both have some downsides in general or to a left handed shooter.

What I was thinking is milling some angled slots into the left side of the upper receiver. The angle would face forward so any gas would blow forward to and to the left. I would bevel the edges on the inside to prevent any snags with the bolt moving back and forth.

Is there anything I should be aware of before attempting this type of a mod?
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Old 10-27-2012, 10:59 AM
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In a direct gas impingement system for the AR your bolt carrier has 2 holes on the right side of the carrier in an indent under the gas key. Those holes are the gas vents that relieve the gas pressure after your bolt has cycled out of battery. They are located there so the gas can easily escape through the ejection port on the right. My concern is that if you start relieving the upper receiver on the left, either A. it will not do anything or B. it will allow some gas to redirect in the opposite direction and cause some unwanted fouling along with a gas signature in both directions to the left and right. I suggest a left handed upper receiver and bolt carrier. We have to remember that high power rifle cartridges operate at pressures of 55,000 psi and higher and playing with the gas system, even the venting could potentially cause issues. Not to say that it wont work but this is just what came to mind. I hope this helps. Another option is converting to a piston system if you go with the .223. This will eliminate all gas signatures to the rear and keep all excess gas forward of the hanguard.
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Old 10-27-2012, 11:39 AM
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Try a PRI gas buster charging handle. It vents the gas from the upper.
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Old 10-27-2012, 12:58 PM
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Quote:
Originally Posted by CIV Tactical View Post
In a direct gas impingement system for the AR your bolt carrier has 2 holes on the right side of the carrier in an indent under the gas key. Those holes are the gas vents that relieve the gas pressure after your bolt has cycled out of battery. They are located there so the gas can easily escape through the ejection port on the right. My concern is that if you start relieving the upper receiver on the left, either A. it will not do anything or B. it will allow some gas to redirect in the opposite direction and cause some unwanted fouling along with a gas signature in both directions to the left and right. I suggest a left handed upper receiver and bolt carrier. We have to remember that high power rifle cartridges operate at pressures of 55,000 psi and higher and playing with the gas system, even the venting could potentially cause issues. Not to say that it wont work but this is just what came to mind. I hope this helps. Another option is converting to a piston system if you go with the .223. This will eliminate all gas signatures to the rear and keep all excess gas forward of the hanguard.
There are some good thought provoking questions there. I was kind of looking at it the same way left hand side charging handles are done similar to ASA, LAR, etc. The reliefs on the left hand side for the charging handle do let gases escape though they have right side ejection. I do have a left handed upper I can use and I am planning on going piston for the .223 SBR and not sure for the .300blk. I bought the lefty AR more as a novelty since all the other ones I have are right handed.

Quote:
Originally Posted by 420ollie View Post
Try a PRI gas buster charging handle. It vents the gas from the upper.
The PRI gas buster ports the gas to the right. The gas comes out right at a lefty shooter's nose. Many of the guys shooting suppressed use silicone to actually create a gasket around the charging handle. I might do some of my own millwork and create a left handed version of the PRI.
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Old 11-02-2012, 11:40 PM
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The purpose for gas buster type charging handles is that suppressors store pressurized gas at the end of the barrel and that gas tends to vent both forward and rearward once the bolt is unlocked.
Rather than trying to fight the gas coming out the rear, just re-time the gas system so that the bolt carrier does not open as quickly.
This will let more gas evacuate out the front which creates a positive flow direction for the rest of the gasses leaving the can.
Carrier timing when combined with cyclic rate timing of the full auto host will make significant reductions to the gas that you feel in the face.
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