AR15 issue

shooter2440 · July 18, 2015, 11:25 PM

Hi there:

This is my third build and the first time I ran into an issue with a build and I would like some input.

So i assembled my upper yesterday and noticed that the BCG sticks out a small fraction of an inch outside the rear of the upper receiver. I closed the rifle anyway and took it to the range today.

I loaded the gun and pressed the trigger and it did not fire. Racked another round and did not fire again.

I took the lower off and put it on another upper and the lower functioned flawless. I took the BCG out and put it in another rifle and it shot just fine.

So I have come to the conclusion that there is an issue with the barrel assembly to the upper receiver. I just don't know what it could be. Any thoughts? I would really appreciate help!

Thank you.

skizzums · July 19, 2015, 01:23 AM

sounds like the lugs on bolt are out of spec. too large

skizzums · July 19, 2015, 01:26 AM

nevermind. reread your post and it sounds like the locks on your barrel are too small, or haedspace is bad. can you try putting the other bolt in the new rifle and see if it closes. if it doesnt, then sounds like a chamner that's too short or ammunition that's too long. but if the ammo is good to go in the other ar, then it sounds like headspace. remove the barrel if possible and do a plunk test and see how well he cartridge drops into the chamber.

can you specify your chamber? wylde, nato etc. what knd of ammo are your using? can you color your bullet top with a sharpie and see if it's jammimg into the lands. outside of that, you will need to get headsace checked. if yo find you chamber hasn't been reamed deep enough, its needs to be sent back asap.

if these are handloads using heavyweight bullets, you could have a rim thickness issue or over-crimping, but proably not the most logical conclusion. first, swap out the bolt from other rifle that you know works. see if it's locks up with out a bullet. then see if it will lock up with a standard 55gr bullet. that should answer some questions

Mobuck · July 19, 2015, 02:13 PM

"I loaded the gun and pressed the trigger and it did not fire. Racked another round and did not fire again."
Did the hammer fall?
Did you lube and hand cycle the BCG 30-40 times before pinning the upper to lower to make sure it was fully seating and locking the bolt into the barrel extension? If the BCG won't slide into battery on it's own with the upper tilted muzzle down at a 45* angle, the upper's not ready to test fire.
There may be some debris in the lug recesses preventing the bolt from fully engaging.

FrankenMauser · July 19, 2015, 04:02 PM

In addition to the above,

Make sure the bolt (removed from BC) can spin in the barrel extension.
Make sure the BCG is functioning properly on its own (not just throwing it in another rifle - see how it's doing independently).

If you're still dead in the water, measure the barrel extension.

It sounds like a bad barrel extension to me. ...But it's worth checking everything else before assuming that the extension is bad, and tearing the upper apart.

TMD · July 19, 2015, 04:49 PM

Either the barrel extension is out of spec or the gas tube is too long. Third thing can be the gas tube isn't aligned and it's hitting the gas key on the bcg.

DnPRK · July 20, 2015, 10:45 PM

My guess is the gas tube roll pin is installed in front of the gas tube and not through the hole in the gas tube.

July 18, 2015, 11:25 PM	#1
shooter2440 Member Join Date: March 4, 2010 Posts: 19	AR15 issue Hi there: This is my third build and the first time I ran into an issue with a build and I would like some input. So i assembled my upper yesterday and noticed that the BCG sticks out a small fraction of an inch outside the rear of the upper receiver. I closed the rifle anyway and took it to the range today. I loaded the gun and pressed the trigger and it did not fire. Racked another round and did not fire again. I took the lower off and put it on another upper and the lower functioned flawless. I took the BCG out and put it in another rifle and it shot just fine. So I have come to the conclusion that there is an issue with the barrel assembly to the upper receiver. I just don't know what it could be. Any thoughts? I would really appreciate help! Thank you.

July 19, 2015, 01:23 AM	#2
skizzums Senior Member Join Date: July 1, 2013 Location: Douglasville, Ga Posts: 4,615	sounds like the lugs on bolt are out of spec. too large __________________ My head is bloody, but unbowed

July 19, 2015, 01:26 AM	#3
skizzums Senior Member Join Date: July 1, 2013 Location: Douglasville, Ga Posts: 4,615	nevermind. reread your post and it sounds like the locks on your barrel are too small, or haedspace is bad. can you try putting the other bolt in the new rifle and see if it closes. if it doesnt, then sounds like a chamner that's too short or ammunition that's too long. but if the ammo is good to go in the other ar, then it sounds like headspace. remove the barrel if possible and do a plunk test and see how well he cartridge drops into the chamber. can you specify your chamber? wylde, nato etc. what knd of ammo are your using? can you color your bullet top with a sharpie and see if it's jammimg into the lands. outside of that, you will need to get headsace checked. if yo find you chamber hasn't been reamed deep enough, its needs to be sent back asap. if these are handloads using heavyweight bullets, you could have a rim thickness issue or over-crimping, but proably not the most logical conclusion. first, swap out the bolt from other rifle that you know works. see if it's locks up with out a bullet. then see if it will lock up with a standard 55gr bullet. that should answer some questions __________________ My head is bloody, but unbowed Last edited by skizzums; July 19, 2015 at 01:31 AM.

July 19, 2015, 04:02 PM	#5
FrankenMauser Senior Member Join Date: August 25, 2008 Location: In the valley above the plain Posts: 13,424	In addition to the above, Make sure the bolt (removed from BC) can spin in the barrel extension. Make sure the BCG is functioning properly on its own (not just throwing it in another rifle - see how it's doing independently). If you're still dead in the water, measure the barrel extension. It sounds like a bad barrel extension to me. ...But it's worth checking everything else before assuming that the extension is bad, and tearing the upper apart. __________________ Don't even try it. It's even worse than the internet would lead you to believe.

July 19, 2015, 02:13 PM	#4
Mobuck Junior member Join Date: February 2, 2010 Posts: 6,846	"I loaded the gun and pressed the trigger and it did not fire. Racked another round and did not fire again." Did the hammer fall? Did you lube and hand cycle the BCG 30-40 times before pinning the upper to lower to make sure it was fully seating and locking the bolt into the barrel extension? If the BCG won't slide into battery on it's own with the upper tilted muzzle down at a 45* angle, the upper's not ready to test fire. There may be some debris in the lug recesses preventing the bolt from fully engaging.

July 19, 2015, 04:49 PM	#6
TMD Senior Member Join Date: August 9, 2011 Posts: 1,293	Either the barrel extension is out of spec or the gas tube is too long. Third thing can be the gas tube isn't aligned and it's hitting the gas key on the bcg.

July 20, 2015, 10:45 PM	#7
DnPRK Senior Member Join Date: August 24, 2001 Location: LC, Ca Posts: 1,917	My guess is the gas tube roll pin is installed in front of the gas tube and not through the hole in the gas tube.