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Having a bit of trouble with a "Colt 604" build. I've assembled a few AR's and haven't run into an issue like this one. The BCG won't clear the end of the top receiver and sit flush. At first i thought something was in the chamber but its clean I also dropped a different BCG into the gun and it sticks out the same length. I am unable to hinge the upper shut. The lugs still rotate, and it head spaces. My thought is that it's an issue with the barrel and chamber. For those that ask the barrel is a Brownell's 20in and BCG is a Browells chrome lined retro one. Not sure what else to try other than reach out to Brownell's and try to get a replacement barrel (the BCG fits in a couple other ARs)

 
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Sumting wong. Is the bcg’s gas tube engaging the upper’s gas tube, and clearing the hole in the charging handle? Is gas tube bent? Any visible burrs on the barrel lugs or bcg lugs? Usually headspace is preset on barrel install… was this premade?
 
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Gas tube not pinned in the hole maybe. I swapped the front sight on a friends rifle for a free float and low profile gas block and i had the same thing happen. The gas tube was too long and stopped the bcg from going forward. It must have moved rearward as i was tapping in the pin, luckily I didnt damage the tube and was a quick fix.
 
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When you say that it headspaces, is that with an assembled rifle? I'm trying to understand if the bolt is fully in battery and locking lugs engaged in the above pics.
 
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Gas tube not pinned in the hole maybe. I swapped the front sight on a friends rifle for a free float and low profile gas block and i had the same thing happen. The gas tube was too long and stopped the bcg from going forward. It must have moved rearward as i was tapping in the pin, luckily I didnt damage the tube and was a quick fix.
Bingo. Ty
 

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