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Posted: 10/31/2016 3:47:01 PM EDT
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This is a 10.5" in barrel from Green Mountain Barrel Company with a carbine length gas system. Here's the link to the exact barrel with specs... http://www.gmriflebarrel.com/gm-m26-10-5-5-56mm-nato-1-7/
I've built several rifles now and have never seen the hole nor what seems to be a pin protruding into the chamber on an AR barrel before. What are these and what is their purpose? Here's the hole in the extension 
Here's the pin, which extends into the chamber area 
Thanks in advance and I'm eager to learn more. -Pete |
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I'm no expert on this, but I saw this other post in regards to a 300 BO cartridge being fired in a 5.56 gun. It was described as an overpressure device and looks a bit like your GM component. Apparently this was a Sig feature if I read correctly. Here's the link, but go to the last page for a pic and description. See what you think.
http://www.ar15.com/forums/t_3_118/703983_Yet_ANOTHER__300_Blackout_round_fired_through_a_5_56_Barrel_pics_of_course_.html&page=4 |
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Quoted:
I'm no expert on this, but I saw this other post in regards to a 300 BO cartridge being fired in a 5.56 gun. It was described as an overpressure device and looks a bit like your GM component. Apparently this was a Sig feature if I read correctly. Here's the link, but go to the last page for a pic and description. See what you think. http://www.ar15.com/forums/t_3_118/703983_Yet_ANOTHER__300_Blackout_round_fired_through_a_5_56_Barrel_pics_of_course_.html&page=4 Unless there is a matching hole in the upper receiver and barrel nut, its use as a overpressure devise is nil. |
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Quoted:
Unless there is a matching hole in the upper receiver and barrel nut, its use as a overpressure devise is nil. Quoted:
Quoted:
I'm no expert on this, but I saw this other post in regards to a 300 BO cartridge being fired in a 5.56 gun. It was described as an overpressure device and looks a bit like your GM component. Apparently this was a Sig feature if I read correctly. Here's the link, but go to the last page for a pic and description. See what you think. http://www.ar15.com/forums/t_3_118/703983_Yet_ANOTHER__300_Blackout_round_fired_through_a_5_56_Barrel_pics_of_course_.html&page=4 Unless there is a matching hole in the upper receiver and barrel nut, its use as a overpressure devise is nil. Lysander, again I'm no expert on this feature, but what I'm getting from the description is that this is not a vent...at least the one in my link post. I can't tell from the OP's pic if that's an "all the way through" hole or if there's a pin or such pressed in there that's not flush with the outer circumference. The Sig component sounds like something that locks the extractor so that the extractor becomes the "weak link" in case of disaster. I'll say again...I'm not personally familiar with this design and never owned one. A cursory check on Sig's site didn't show me anything about it, so I have no idea. Frankly I'd be surprised that GM would have this feature manufactured into their barrel at this price point, but I can't swear to that. I have a GM 416R SS 10.5" barrel on a pistol AR that I'm pretty impressed with for its price point. However, mine doesn't have that hole. |
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Quoted:
Here's what Green Mountain had to say... Quoted:
Here's what Green Mountain had to say... The extension on the GM-M26 has an extractor support pin and the hole on the opposite side is how they install the extractor support pin. This will not affect the performance of your build. That's interesting. I've never seen or at least noticed it in other AR15 barrels. After this thread I've read more about the "extractor support pin". It seems to be more useful on guns that are overgassed and/or full auto. Apparently it hurts nothing, so no harm no foul...at least from what I've gleaned from reading up on some of it. |
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