AR BCG troubles

Nottherealfranco · Dec 30, 2014

Hey all,

Attempting my first AR build, and i'm running into a little issue. My BCG seems to be sticking out of the back of my upper ever so slightly, preventing the upper from pivoting onto the lower. BCG fits well inside the upper, and clicks firmly into place, however it is not sitting flush with the back of the receiver.

Pictures:

Any help or suggestions is appreciated.

Thank you

Fox123 · Dec 30, 2014

When you press the forward assist does it close any further?

Does the bolt fully cam rearward out of the receiver?

What brand is everything?

lee2 · Dec 30, 2014

can you push the bolt fully back into the bolt carrier group?
try removing the bolt from the bolt carrier and see if the carrier fits flush into the upper receiver.

Erick · Dec 30, 2014

Fox123 said:
When you press the forward assist does it close any further?

Does the bolt fully cam rearward out of the receiver?

What brand is everything?

What he said.

I apologize if this is too banal an explanation but occasion when I am in a hurry to close a rifle in the field I find the need to push the BCG in as it can stick out a bit.

it doenst happen often though the only other explanation I think think of is so badly out of spec upper or BCG that I cannot imagine it.. .

Nottherealfranco · Dec 30, 2014

Fox123 said:
When you press the forward assist does it close any further?

Does the bolt fully cam rearward out of the receiver?

What brand is everything?

Pressing the forward assist does nothing. I don't quite understand what you mean by "cam rearward". Upper I bought as a complete upper with the bcg and charging handle from JSE surplus, lower is an anderson lower.

jkeys · Dec 30, 2014

As already said, hit the forward assist and see if that fixes it. If not, pull the bolt out of the carrier and make sure the carrier slides in all the way. I would recommend borrowing or buying a headspace gauge set so you know the parts are in spec before you shoot the gun. It is a $40 safety measure that is cheaper than a broken gun or trip to the hospital.

Nottherealfranco · Dec 30, 2014

lee2 said:
can you push the bolt fully back into the bolt carrier group?
try removing the bolt from the bolt carrier and see if the carrier fits flush into the upper receiver.

After removing the bolt from the bcg, the bcg still does not sit flush with the upper.

Is this a gas tube issue then?

dontpanic · Dec 30, 2014

Nottherealfranco said:
After removing the bolt from the bcg, the bcg still does not sit flush with the upper.

Is this a gas tube issue then?

Looks like it could be. Wrong length gas tube? Possibly a mid in a carbine system.

If you look inside your upper receiver and see about 1.5in of gas tube then that is your problem

Edit. Just saw the picture inside your receiver. See if your gas tube is bent?

Boom Boom · Dec 30, 2014

Assuming the bolt is assembled correctly, it looks like the bolt lugs are not seating correctly in the barrel extension. It can be a tight fit on a new rifle, meaning you have to give the back of the carrier a good push to fully seat the lugs. In your photo of the barrel extension, what's the debris? Hopefully dust and not sand. It also looks bone dry. Lube is your friend on AR rifles.

Nottherealfranco · Dec 30, 2014

dontpanic said:
Looks like it could be. Wrong length gas tube? Possibly a mid in a carbine system.

If you look inside your upper receiver and see about 1.5in of gas tube then that is your problem

Edit. Just saw the picture inside your receiver. See if your gas tube is bent?

The gas tube doesn't appear to be bent at all, at least not that i can tell.

Boom Boom said:
Assuming the bolt is assembled correctly, it looks like the bolt lugs are not seating correctly in the barrel extension. It can be a tight fit on a new rifle, meaning you have to give the back of the carrier a good push to fully seat the lugs. In your photo of the barrel extension, what's the debris? Hopefully dust and not sand. It also looks bone dry. Lube is your friend on AR rifles.

I've removed the bolt from the carrier and it still is not seating fully. The debris you're seeing is dust that was picked up due to the macro setting i used on the camera. The receiver is very dry, but that shouldn't affect the fitment of the bcg should it?

clandestine · Dec 30, 2014

Its not the barrel extension or bolt. The gas tube is too long.

That upper is FUBAR anyway. Those dremeled ramps are cheese grater, and likely are clickers. Send that thing back.

I have seen enough of that brand of uppers with bad headspace to never trust one unless I guaged it out completely.

Here's what protrusion you should get on your gas tube when the charging stem is locked in. Yes that's an AR cut away.

Boom Boom · Dec 30, 2014

Bone dry can make the bolt lugs tough to seat on a brand new rifle. If the empty carrier won't seat, you can probably see or feel about where the interference is. I'm inclined to think it's the gas tube or forward assist. Is the forward assist spring working, meaning does the assist stay popped out so it doesn't hit the carrier?

Edit: Clandestine posted your answer.

Nottherealfranco · Dec 31, 2014

clandestine said:
Its not the barrel extension or bolt. The gas tube is too long.

That upper is FUBAR anyway. Those dremeled temps are cheese grater, and likely are clickers. Send that thing back.

I have seen enough of that brand of uppers with bad headspace to never trust one unless I guaged it out completely.

I'm afraid I don't follow.. Dremeled temps? clickers?

I bought this as a 'blemished' item.. I don't know if i can return it...

clandestine · Dec 31, 2014

Here's how much space you have in the gas key when it's in battery.

clandestine · Dec 31, 2014

Nottherealfranco said:
I'm afraid I don't follow.. Dremeled temps? clickers?

I bought this as a 'blemished' item.. I don't know if i can return it...

Sorry, it was a typo. Dremeled feel ramps is what I meant. They are not even or smooth, and a clicker refers to the upper barrel extension Ramps slightly overhanging the lower ramps like a roof shingle. When this happens it can cause bullet setback and failures to feed.

Nottherealfranco · Dec 31, 2014

Is it possible for my bcg to be out of spec? It looks like it's coming in full contact with the front of the receiver.. If there was a gas tube issue wouldn't the bcg not fully seat?

clandestine · Dec 31, 2014

The upper can be fixed but I would get it checked out. Replace the gas tube with the proper length one, have the headspace checked, and have a skilled AR guy/gal clean those ramps up. The lower ramps should not have been ground at all, removing the anodizing is not good because it's where all oF the hardness lies on the aluminum ramps.

Boom Boom · Dec 31, 2014

clandestine said:
Sorry, it was a typo. Dremeled feel ramps is what I meant. They are not even or smooth

That's what my dust question was getting at.

What he thinks is dust might be leftover metal filings.

clandestine · Dec 31, 2014

Nottherealfranco said:
Is it possible for my bcg to be out of spec? It looks like it's coming in full contact with the front of the receiver.. If there was a gas tube issue wouldn't the bcg not fully seat?

When you removed the bolt head and inserted just the carrier into the upper it still sticks out right? If so the gas tube is bottoming out inside the gas key on the bolt carrier. If you look at my cut away bolt youll see that there has to be a space, if not it shuts the gas system off. Even if you got it to slam close it wouldn't cycle because it's going to crimp the end of the gas tube, blocking off the relief port in the carrier that causes the bolt head to unlock under pressure. Someone put a mid gas or custom length gas tube in a carbine upper gas system, or the like.

clandestine · Dec 31, 2014

Boom Boom said:
That's what my dust question was getting at. What he thinks is dust might be leftover metal filings.

Yup, looks like someone jacked it up and dI don't even bother cleaning out their dremel work.

AR BCG troubles

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