First time shooting new AR, BCG won't extract or load properly.

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chris*1989

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I just finished building my frankenstein AR15 (Problem #1), and the BCG is having a problem.
If I give the charging handle a good rack, it'll chamber a round, however if I just hit the slide release, it won't push the BCG with enough force to load a round.
Same thing with extracting, the BCG will stop about half way with a casing in its grip.

I originally had a thin coat of high temp grease on the BCG and worked it through the upper receiver a couple times. I cleaned the grease off the BCG after it not working, and just used a good coating of oil, and still the same thing, a lot of friction from what I'm assuming is the upper reciver. All the parts are brand new and haven't been broken in yet.

Any ideas?

stupidgun_zps5c5a4c12.jpg
 
The upper is a YHM and the bolt is a Titanium Nitride coated DPMS.
There's a little bit of rubbing on the usual wear points, but nothing that looks like it's scratching or rubbing hard (yet). I only put about 10 rounds through trying to figure it out.
I swapped BCG's with my Colt, and same thing on the new gun with a Colt BCG in it. And the DPMS BCG works perfectly in the Colt rifle, which made me think it was the new Upper that was the issue.

Pigeonman said:
If you pull the bolt from the upper do you see any obvious signs of rubbing? What make are the upper and BCG?
Click to expand...
 
Greenhorse six said:
How well does the bolt move in the upper with the upper off the lower?
Click to expand...

This could be an important difference. If it moves fine without being attached to the upper, it could be a buffer/spring issue If not, I would check that the gas tube isn't bent and that the gas key is engaging the gas tube properly. With the upper separated it should be easy to see.
 
How does it feel when cocking it without a mag in it? Any binding at all through the travel? If so I would look at buffer, spring or buffer tube. Or clearances in the upper being out of spec. Look for wear inside the upper as the anodized layer is thin, and if it's binding up that bad it'll wear through quite quickly.

If there is no binding without a mag, but hangs up with a mag something could be amiss with your BHO.
 
I checked the gas tube and the key and they mesh perfectly.

When I pulled the bottom receiver off, the bcg still had some resistance moving all the way back and locking forward. I tried taking the bolt out of the carrier and the carrier moved a little more freely. When I bought the bcg from Milarm they told me they used a different brand of bolt, however I tried another one and had the same problem in the gun. The common denominator seems to be the feed ramps on the barrel slowing the bcg down moving in both directions. Does it sound plausible?
The barrel is a 14.5 NEA.
 
Does the bolt carrier move smoothly through without ammunition. If inverted and released will the BGC move through the upper?
If not, I'd guess a squashed upper receiver.
Did you use a proper AR15 action block to hold the receiver while you torqued the barrel nut?
 
Yeah. I was doing all my tests without a magazine or ammo in and still some resistance. I used the vice block that clamps over the outside of the receiver.


dangertree said:
Does the bolt carrier move smoothly through without ammunition. If inverted and released will the BGC move through the upper?
If not, I'd guess a squashed upper receiver.
Did you use a proper AR15 action block to hold the receiver while you torqued the barrel nut?
Click to expand...
 
Wasn't there another thread where the NEA barrel feed ramps were totally off centre and the bolt would't fit in at all? Can you take a picture under the upper with the bolt just backed up behind the feed ramps? Do they look like they should line up correctly?
 
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