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Joined: Jan 2009
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OP
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I have a ar 308 Dpms upper with with an 18 inch x-caliber 358 win barrel with an Anderson adjustable gas block. Problem is it is not cycling correctly. I have the gas block wide open and i am running the bolt sloppy wet with oil. It will cycle with no mag in this state but will not cycle reliability with a mag in. It also just dripples the ejected case out on the ground when it does Cycle. The gas port size is just .067. From what I am reading this seems small, but can't get / find anything that says what the usual size for this round should be. Any one with any ideas?
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Joined: Mar 2004
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Campfire Outfitter
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Campfire Outfitter
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No idea. Gas port sizes seem to be kept pretty tight by the mfgrs.
The 20" 223 NM barrels I get seem to all have .093" (#42 drill) gas ports. IIRC, I think I've been opening the to a #40 or 41 (.096" or 98).
John Burns said that mil spec for the 18 inch Rifle Length Gas System port is 0.105 for Crane built Mk 12s. He likes 0.110 better as there is not much lee way for cold weather or dirty guns at 0.105.
And it depends upon the powders you use too. I get excellent function with powders like Varget and Re15, but it's hard to get good function with stuff like WC844 or 846 in my match guns.
With an adjustable gas block, you can drill them large and throttle them back.
Islam is a terrorist organization.
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Joined: Sep 2006
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Campfire Regular
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I run .110 on my 16" rifle length gas 5.56 barrels and have NEVER had a issue. I would open it up to .110 and if need be tune it down with your adjustable gas block.
All the best things in life, live on the other side off fear.
The true eye sees not the despair of its victims, only the elegance of equilibrium. It's a demonstration of superior judgment.
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Joined: Mar 2005
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Campfire Tracker
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.067 seems small. I want to say my BHW .308 barrel came as .095 and was opened to .105 which has been flawless.
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Joined: Nov 2011
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Campfire 'Bwana
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Campfire 'Bwana
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.067 seems small. I want to say my BHW .308 barrel came as .095 and was opened to .105 which has been flawless. .067 is small. Typical 5.56 gas port sizes usually ranges between .06 and .10
You didn't use logic or reason to get into this opinion, I cannot use logic or reason to get you out of it.
You cannot over estimate the unimportance of nearly everything. John Maxwell
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I have a ar 308 Dpms upper with with an 18 inch x-caliber 358 win barrel with an Anderson adjustable gas block. Problem is it is not cycling correctly. I have the gas block wide open and i am running the bolt sloppy wet with oil. It will cycle with no mag in this state but will not cycle reliability with a mag in. It also just dripples the ejected case out on the ground when it does Cycle. The gas port size is just .067. From what I am reading this seems small, but can't get / find anything that says what the usual size for this round should be. Any one with any ideas? None of the sizes people will post here about their 308 or 5.56 barrels have any relevance to the port size you need for a 358 Win barrel. Obviously it needs to be larger, but none of us know how much. The larger bore makes the gas port size and location requirements different than a 308 barrel. Unfortunately it sounds like X-caliber tried to just use 308 specs without fully understanding the effect of the case/bore ratio difference. How long is your barrel, and what is the gas system length?
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Joined: Jan 2009
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OP
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It is an 18 inch barrel with a mid length gas port.
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Joined: Jul 2015
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Campfire Outfitter
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Anybody know what port size 300 Blk barrels have been coming with?
Politics is War by Other Means
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Joined: Jan 2009
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I took mine out to . #43 .089 runs fine now.
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Joined: Nov 2011
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Campfire 'Bwana
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Campfire 'Bwana
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I took mine out to . #43 .089 runs fine now. Good to hear. Nice to know what made it work.
You didn't use logic or reason to get into this opinion, I cannot use logic or reason to get you out of it.
You cannot over estimate the unimportance of nearly everything. John Maxwell
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Glad it worked out for you.
All the best things in life, live on the other side off fear.
The true eye sees not the despair of its victims, only the elegance of equilibrium. It's a demonstration of superior judgment.
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