Ar 15 expert help!

SwayV7 · February 13, 2015, 08:46 PM

Ok guys, hate to beat the dead horse but I could really use some help. Ar 15 mrk 12. 20" barrel rifle length gas system SHORT STROKE ISSUE. Im NOT NEW TO THE AR PLATFORM... Common symptoms, FFT/Bolt will not lock back. Short stroke issue with every kind of factory ammo, & hand loads. Running small base dies with hand loads.
1) Ar is properly cleaned and lubed

2) tried 3 different buffer springs (eliminate bolt "bounce")

3) tried all buffers from standard to H3. (adjustable stock, running carbine buffers. *FFT issue resolve, but bolt will not lock back consistently with lighter buffers. it came with an H3.

4) Checked gas key/rings. And even ran a bcg from another rifle. Same issue.

5) Checked alignment of gas block and gas tube.

Now I am debating on opening the gas port on the barrel another size up... Thoughts and concerns, Maybe I missed something? This issue has me pulling my hair out, never had this issue with any ar I have ever owned. ANY advise or help would be greatly appreciated!

skizzums · February 13, 2015, 09:18 PM

sounds like a gas block issue of some kind. I know you said you have checked the alignment, but sometimes the hole is just a hair out of alignment. I run into the prob from time to time with one in particular AR, and I just have to bring a tool set with me and keep moving it until I get it right. but your not going to hurt much by opening it up just a hair either. but I don't know what else the problem could be.

SwayV7 · February 13, 2015, 09:27 PM

I guess the gas block is the only thing I have not changed out or tried moving around... Im running a pri gas block w flip up sight. If I open up the gas port on the barrel, will it leave burrs on the inside of the barrel? That is the only thing holding me back from doing it... I have a wood dial already in place so that the bit will not hit the inside if the barrel when it goes thru. Just in case I slip up and go too far.

marine6680 · February 13, 2015, 10:32 PM

20 inch barrel upper on a M4 type adjustable stock lower?

The Action/recoil spring on the adjustable stock is stronger than that of a fixed stock... Still short strokes with light weight buffers?

Tripple check the gas block.

SwayV7 · February 13, 2015, 10:46 PM

Yes I tested with standard buffer, h, h2,h3. Also tested 3 springco springs from there standard white, blue and red.

Metal god · February 14, 2015, 01:33 AM

Did you install the gas block ??

I just finished a NM build that I had to line the front sight base up with the gas port . Other builds I just pushed to gas block back till it stoped and secured the set screw and others had the taper pins . On this match barrel and front sight base with adjustable windage screws I had to line it all up . I measured , checked , rechecked then measured again before installing the front sight base . I even wrote down all the measurements to keep track . Went to the range and had your same problem . Came home pulled the front sight base off and started measuring again . "WHAT"

I was off , I missed it by close to .030 front to back . Not really sure what I was looking at or measuring the first time but the gun is flawless now .

I'd check that front sight base/block first before drilling out the port . What make is the barrel and front sight base ?

SwayV7 · February 14, 2015, 02:00 AM

I bought the AR from a gunsmith, the gas block was already installed when I got it. Its a bartlein or white oak barrel. I e mailed the gunsmith for barrel specs. I wont mention his name until I figure out what the issue is

! As of right now im not too happy, and it maybe something where he may not be at fault so im holding off t'll I fix it. I have only removed it and reinstalled once to check the aliment. But I will check one more time... I measured and marked the sight before I removed it so I would have a second reference to where it was positioned originally. My measurement lined up spot on to where I marked it from its original install. If this AR didn't shoot lights out I would be more than willing too give up and call quits or send it back. I am getting under .5moa with my hand loads. Who would figure that the most accurate AR I have ever owned would be such a pain!!!

noonesshowmonkey · February 14, 2015, 03:15 AM

A heavier buffer won't make a short stroking gun not short stroke. Sounds under-gassed, and like you either have a poorly seated gas block, a small gas port on the barrel, or serious fouling in one or both.

Mobuck · February 14, 2015, 07:32 AM

Some gas blocks are designed to align correctly with the forward hand guard retainer in place. W/o this the gas block may not line up correctly.
FWIW
Rifle length uppers on carbine lowers is a non-issue. Using a heavier buffer is counter action to the problem you describe. Check to make sure there's not some foreign material lodged in the end of your buffer tube.

stagpanther · February 14, 2015, 03:27 PM

I'm no expert--but I've built a few--in a way it's a good thing it's happening to all your rounds--it's probably something that is profoundly off would be my guess, which is usually a bit easier to find and correct than the "once in a while and only with xxx" type of problem. If you eliminate gas and buffer problems--my next place to look would be the bolt and extension/feed ramps. Are you sure headspacing is correct, bolt lock-up is correct and there are no issues between chambering and extraction? Do the spent cases show anything unusual?

You mentioned it's a custom barrel--could possibly be some issues there depending on who did the bore/reaming. Just throwing some ideas out there. Consider it valuable learning and it won't be so bad or frustrating. As usual--my less than 2 cents with a healthy dose of salt. : )

February 13, 2015, 08:46 PM	#1
SwayV7 Member Join Date: December 6, 2012 Location: NM Posts: 17	Ar 15 expert help! Ok guys, hate to beat the dead horse but I could really use some help. Ar 15 mrk 12. 20" barrel rifle length gas system SHORT STROKE ISSUE. Im NOT NEW TO THE AR PLATFORM... Common symptoms, FFT/Bolt will not lock back. Short stroke issue with every kind of factory ammo, & hand loads. Running small base dies with hand loads. 1) Ar is properly cleaned and lubed 2) tried 3 different buffer springs (eliminate bolt "bounce") 3) tried all buffers from standard to H3. (adjustable stock, running carbine buffers. *FFT issue resolve, but bolt will not lock back consistently with lighter buffers. it came with an H3. 4) Checked gas key/rings. And even ran a bcg from another rifle. Same issue. 5) Checked alignment of gas block and gas tube. Now I am debating on opening the gas port on the barrel another size up... Thoughts and concerns, Maybe I missed something? This issue has me pulling my hair out, never had this issue with any ar I have ever owned. ANY advise or help would be greatly appreciated! __________________ "If I should perish in the defense of liberty, let it be known, I died a free man"

February 13, 2015, 09:18 PM	#2
skizzums Senior Member Join Date: July 1, 2013 Location: Douglasville, Ga Posts: 4,615	sounds like a gas block issue of some kind. I know you said you have checked the alignment, but sometimes the hole is just a hair out of alignment. I run into the prob from time to time with one in particular AR, and I just have to bring a tool set with me and keep moving it until I get it right. but your not going to hurt much by opening it up just a hair either. but I don't know what else the problem could be. __________________ My head is bloody, but unbowed

February 13, 2015, 09:27 PM	#3
SwayV7 Member Join Date: December 6, 2012 Location: NM Posts: 17	I guess the gas block is the only thing I have not changed out or tried moving around... Im running a pri gas block w flip up sight. If I open up the gas port on the barrel, will it leave burrs on the inside of the barrel? That is the only thing holding me back from doing it... I have a wood dial already in place so that the bit will not hit the inside if the barrel when it goes thru. Just in case I slip up and go too far. __________________ "If I should perish in the defense of liberty, let it be known, I died a free man"

February 13, 2015, 10:46 PM	#5
SwayV7 Member Join Date: December 6, 2012 Location: NM Posts: 17	Yes I tested with standard buffer, h, h2,h3. Also tested 3 springco springs from there standard white, blue and red. __________________ "If I should perish in the defense of liberty, let it be known, I died a free man"

February 14, 2015, 01:33 AM	#6
Metal god Senior Member Join Date: April 10, 2012 Location: San Diego CA Posts: 6,876	Did you install the gas block ?? I just finished a NM build that I had to line the front sight base up with the gas port . Other builds I just pushed to gas block back till it stoped and secured the set screw and others had the taper pins . On this match barrel and front sight base with adjustable windage screws I had to line it all up . I measured , checked , rechecked then measured again before installing the front sight base . I even wrote down all the measurements to keep track . Went to the range and had your same problem . Came home pulled the front sight base off and started measuring again . "WHAT" I was off , I missed it by close to .030 front to back . Not really sure what I was looking at or measuring the first time but the gun is flawless now . I'd check that front sight base/block first before drilling out the port . What make is the barrel and front sight base ? __________________ If Jesus had a gun , he'd probably still be alive ! I almost always write my posts regardless of content in a jovial manor and intent . If that's not how you took it , please try again .

February 13, 2015, 10:32 PM	#4
marine6680 Senior Member Join Date: July 24, 2012 Location: Parker, CO Posts: 4,594	20 inch barrel upper on a M4 type adjustable stock lower? The Action/recoil spring on the adjustable stock is stronger than that of a fixed stock... Still short strokes with light weight buffers? Tripple check the gas block.

February 14, 2015, 02:00 AM	#7
SwayV7 Member Join Date: December 6, 2012 Location: NM Posts: 17	I bought the AR from a gunsmith, the gas block was already installed when I got it. Its a bartlein or white oak barrel. I e mailed the gunsmith for barrel specs. I wont mention his name until I figure out what the issue is ! As of right now im not too happy, and it maybe something where he may not be at fault so im holding off t'll I fix it. I have only removed it and reinstalled once to check the aliment. But I will check one more time... I measured and marked the sight before I removed it so I would have a second reference to where it was positioned originally. My measurement lined up spot on to where I marked it from its original install. If this AR didn't shoot lights out I would be more than willing too give up and call quits or send it back. I am getting under .5moa with my hand loads. Who would figure that the most accurate AR I have ever owned would be such a pain!!! __________________ "If I should perish in the defense of liberty, let it be known, I died a free man"

February 14, 2015, 03:15 AM	#8
noonesshowmonkey Senior Member Join Date: April 19, 2014 Posts: 329	A heavier buffer won't make a short stroking gun not short stroke. Sounds under-gassed, and like you either have a poorly seated gas block, a small gas port on the barrel, or serious fouling in one or both.

February 14, 2015, 07:32 AM	#9
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	Some gas blocks are designed to align correctly with the forward hand guard retainer in place. W/o this the gas block may not line up correctly. FWIW Rifle length uppers on carbine lowers is a non-issue. Using a heavier buffer is counter action to the problem you describe. Check to make sure there's not some foreign material lodged in the end of your buffer tube.

February 14, 2015, 03:27 PM	#10
stagpanther Senior Member Join Date: March 2, 2014 Posts: 11,792	I'm no expert--but I've built a few--in a way it's a good thing it's happening to all your rounds--it's probably something that is profoundly off would be my guess, which is usually a bit easier to find and correct than the "once in a while and only with xxx" type of problem. If you eliminate gas and buffer problems--my next place to look would be the bolt and extension/feed ramps. Are you sure headspacing is correct, bolt lock-up is correct and there are no issues between chambering and extraction? Do the spent cases show anything unusual? You mentioned it's a custom barrel--could possibly be some issues there depending on who did the bore/reaming. Just throwing some ideas out there. Consider it valuable learning and it won't be so bad or frustrating. As usual--my less than 2 cents with a healthy dose of salt. : )