AR BCG hanging up on stock tube

[Will Learn]

When I pull the charging handle back the bolt hangs up on the stock tube (I think). I have to pull the handle back and up for it not to catch. I'm thinking i just need to unscrew the tube a bit but wanted to get a 2nd opinion. Kind of a PITA as it's happening on my registered SBR lower. :banghead:

 

[waterhouse]

Have you used other uppers on this lower that worked, or is the lower pretty much brand new to you?

 

[Coronach]

Take a look at the inside of the receiver extension (buffer tube). Is the extension holding down the end of the buffer retainer plunger properly?

Mike