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Posted: 12/10/2013 9:12:17 AM EST
Hi all-

I am extremely new to the hobby so bare with me. I finished my build:
AeroPrecision upper and lower
RRA single stage trigger
Spikes Tact BCG
RRA butstock kit
http://www.rockriverarms.com/index.cfm?fuseaction=category.display&category_id=392
16" 1:7 Barrel from Brownells (0.750" at gas port)
http://www.brownells.com/rifle-parts/barrel-parts/rifle-barrels/ar-15-m16-hammer-forged-carbine-barrel-16-carbine-barrel-sku100-008-908-45463-101856.aspx

I took the gun to the range this weekend and fired off 200+ rounds like a bolt action gun. The BCG would not re-cock itself....no movement whatsoever, not even on last round.

I disassembled the firearm last night and here are some things that i found:
1. gas port hole in barrel is 1/16" so i don't think that is the problem
2. gas tube at end which goes into gas block was covered in carbon
3. gas tube at end which goes into BCG was covered in carbon

My initial diagnosis is that the marriage between the gas tube and the gas block sucks and pressure is escaping. Can anyone help?

If my theory is correct, i will need to purchase a new gas block and gas tube....as i failed at my first attempt, can someone point me to one that will work?

Thanks in advance for the help!
a

Link Posted: 12/10/2013 9:23:20 AM EST
There will always be a little leakage until it builds up enough carbon to fully seal.... But not enough to keep it from functioning.
Are you certain that the gas block it lined up with the gas port? Is the gas port properly located... top dead center of the barrel? Make sure it's at 12 o'clock. Is the gas block too far forward of back of the gas port so there isn't enough gas going into the gas block and tube?
Link Posted: 12/10/2013 9:33:35 AM EST
[Last Edit: 12/10/2013 9:36:03 AM EST by Gamma762]
https://www.google.com/#q=%22short+stroking%22+site:ar15.com

Might take a look though some of the previous thousand or so short stroking threads.

Why did you shoot 200 rounds though an obviously malfunctioning rifle?

With what you describe, if you get NO movement at all, you have complete gas system blockage. If you have carbon on the gas tube at the receiver end I'd suspect your bolt carrier doesn't have a gas port. Try swapping in a known working BCG and see if it works. If that's not it the next places I would look would be at gas block alignment to the gas port (especially the often overlooked forward/backwards alignment) and to make sure the gas tube is not upside down.
Link Posted: 12/10/2013 1:06:00 PM EST
the gas block was installed at exactly 12 o'clock and the holes were lined up. i know because of the circle of carbon around the gas port when i removed the block.

i believe my BCG has a gas port, but am not sure...can you explain what that is? If it is the tube on top of the BCG where the gas tube connects with the BCG then the answer is yes, my BCG has that.

to answer your question why i shot that many rounds...... well, this was the first time i shot a rifle period and had to drive 2 hrs to get to an outdoor range to do so. i knew i might run into this problem but i didnt care, i was out shooting a firearm i built myself and honestly didnt care.

Now im troubleshooting
Link Posted: 12/10/2013 2:03:00 PM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By BarneyRubbles:
i believe my BCG has a gas port, but am not sure...can you explain what that is? If it is the tube on top of the BCG where the gas tube connects with the BCG then the answer is yes, my BCG has that.
View Quote

The hole between the gas key and the inside of the bolt carrier. Gas has to flow from the tube, through the key, through the hole, into the little chamber inside the BCG, where it pushes the bolt and carrier apart.

See:
http://www.ar15.com/forums/t_2_130/165511_How_the_Piston_in_your_DI_AR_works.html&page=1

Just to the right of the piston rings you can just make out the hole in the top, which leads up to the back of the gas key.

Disassemble the BCG and pour some liquid into the gas key and see if it flows into the carrier.
Link Posted: 12/10/2013 2:49:22 PM EST

Pull the bolt forward, put lips to gas ken and blow. That should tell you if your gas port is there or obstructed.

Are you sure you installed the gas tube correctly? Did you line the hole in the tube with the hole in the gas block? Then tap in the roll pin?

Link Posted: 12/10/2013 2:51:20 PM EST
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Gamma762:

The hole between the gas key and the inside of the bolt carrier. Gas has to flow from the tube, through the key, through the hole, into the little chamber inside the BCG, where it pushes the bolt and carrier apart.

See:
http://www.ar15.com/forums/t_2_130/165511_How_the_Piston_in_your_DI_AR_works.html&page=1
http://www.adcofirearms.com/junkpics/locked-un.jpg
Just to the right of the piston rings you can just make out the hole in the top, which leads up to the back of the gas key.

Disassemble the BCG and pour some liquid into the gas key and see if it flows into the carrier.
View Quote View All Quotes
View All Quotes
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Gamma762:
Originally Posted By BarneyRubbles:
i believe my BCG has a gas port, but am not sure...can you explain what that is? If it is the tube on top of the BCG where the gas tube connects with the BCG then the answer is yes, my BCG has that.

The hole between the gas key and the inside of the bolt carrier. Gas has to flow from the tube, through the key, through the hole, into the little chamber inside the BCG, where it pushes the bolt and carrier apart.

See:
http://www.ar15.com/forums/t_2_130/165511_How_the_Piston_in_your_DI_AR_works.html&page=1
http://www.adcofirearms.com/junkpics/locked-un.jpg
Just to the right of the piston rings you can just make out the hole in the top, which leads up to the back of the gas key.

Disassemble the BCG and pour some liquid into the gas key and see if it flows into the carrier.


That's a great thread with great photos.

It should be required reading for new members.

Link Posted: 12/10/2013 3:07:10 PM EST
Check your buffer and buffer tube for strange wear.
Link Posted: 12/12/2013 10:43:20 AM EST
I checked the BCG and blew through it....tasted like crap but it is not obstructed.

I think the problem is the gas tube and gas block and really, that I bought a shitty gas block as the gas tube jiggles when it is in there.

Can anyone recommend a good gas block for my barrel and where to get a good gas tube.

I realize this is a dumb question but i dont want to mess around with this anymore.

thanks again for all the help.
Link Posted: 12/12/2013 11:56:34 AM EST
It seems to me that even if the gas key was not ported, that the gas impetus would blow the bolt carrier back anyway. Did you probe the gas port in the barrel to see if it were partly obstructed with steel shavings from when it was drilled?
Link Posted: 12/12/2013 12:05:51 PM EST
[Last Edit: 12/12/2013 12:07:08 PM EST by Gamma762]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By BarneyRubbles:
Can anyone recommend a good gas block for my barrel and where to get a good gas tube.
View Quote View All Quotes
View All Quotes
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By BarneyRubbles:
Can anyone recommend a good gas block for my barrel and where to get a good gas tube.

Does your barrel have a dimple on the underside for a set screw? If so a set screw type block is appropriate, if not, a clamp style would be better.

If the gas tube does not fit snug in the block you're probably losing so much gas as to prevent function.

Originally Posted By 1saxman:
It seems to me that even if the gas key was not ported, that the gas impetus would blow the bolt carrier back anyway.

No, an AR15 doesn't work that way.
Link Posted: 12/12/2013 12:26:23 PM EST
You know I have to try it and see. :)
Link Posted: 12/12/2013 12:47:18 PM EST
inb4 move to troubleshooting
Link Posted: 12/12/2013 1:14:12 PM EST
I've had gas tubes that had obstructions in them. Run a peice of tie wire through it and make sure it's clear. Then blow some compressed air through it. Also do the same for the gas key.
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