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 Post subject: AR15 failure to function with .223
New postPosted: May 18th, 2017, 8:29 pm 
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NEWBIE! (<10 posts)
NEWBIE! (<10 posts)

Joined: November 6th, 2011, 10:24 pm
Posts: 9
Hi,hoping someone can help me out. AR15 build won't eject or feed next round when using .223, but when using 5.56 worked fine, what could be causing this? Using only AE223 OR PMC bronze. Everything functions fine in my Colt and DPMS, but not this. All new parts aND only fired about 50 rounds.Any help would be appreciated.


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 Post subject: Re: AR15 failure to function with .223
New postPosted: May 18th, 2017, 9:04 pm 
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AZS; Woohoo!
AZS; Woohoo!
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Joined: March 28th, 2005, 5:54 pm
Posts: 1655
Location: West of west Phoenix
5.56 is a bit hotter, sounds like not enough gas or some strange issue with the buffer tube/sprin/buffer?
I had a canted buffer tube once that would bind up on the bcg just enough to fail to cycle.
Try swapping the lower and upper with another upper and lower, test fire, if issue persists my bet is on gas port issue of some sort.

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 Post subject: Re: AR15 failure to function with .223
New postPosted: May 19th, 2017, 6:00 am 
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AZS Addict
AZS Addict

Joined: June 4th, 2011, 7:48 am
Posts: 803
Location: NW Valley
I'd agree with the gun being under gassed. You might want to buy an adjustable gas block and install that in place of the one you have. You can dial in the right amount of gas and not more than you need. This will keep recoil to a minimum and should solve the issue with not shooting .223. I do the adjustment while shooting .223 since that will then also work with the hotter 5.56. There is a chance that the gas port is too small. If so, you can drill it out a very little bit and try again.

You might try switching out the buffer spring or the buffer like mentioned above. That would certainly be worth doing prior to spending money on the adjustable gas block. Switching to a different lower would also tell you if the problem is with the upper or lower. If you find that it is the upper, my bet is with the gas port possibly being too small. I bought an AR Stoner barrel from Midway and had to drill out the gas port to get it to cycle.


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 Post subject: Re: AR15 failure to function with .223
New postPosted: May 21st, 2017, 2:57 pm 
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AZS is my home
AZS is my home
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Joined: December 27th, 2008, 4:06 pm
Posts: 11826
Ok, let's look at this as we should be. OP says it is a build, not a factory gun. Before everyone runs out suggesting adjustable gas blocks, blah blah blah, let's consider the following:

1. is the barrel a COTS barrel? Depending on the intended use will assume the gas port is correct.

That said, look first to the following:
a. have you fired it with GI ammo? If yes does it cycle correctly? If no, then look to the following:
b. is the gas block (or FSB) properly indexed and set back? This is the most common problem I see; any kind of a cant or not set back all the wall will be just enough to cause short stroking. I have personal experience here.
c. If the gas block / FSB is properly set is the gas tube seated correctly? Have seen that issue
d. working back, is the BCG key seated and tightened correctly? If you did it right there is no need to stake. If you feel the need and must the use a drop or 2 of green loctite
e. does the gas tube enter the key correctly and is there any damage to the tip? Is there anything IN the tube or the key? Believe it or not, Bill Poole has a blown primer inside the key on his rifle.
f. are the gas rings aligned correctly? are they new or used?

I will ask additional questions later but let's look at the above first before spending any money unnecessarily. Oh, tell us a little more about the build: SBR, carbine, mid-length, full size rifle?


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