I would remove the bolt, cam pin and firing pin. With the charging handle in place Id slide the bolt carrier into the upper receiver. If the carrier in not binding in the upper Id look closely at the bolt for any wear marks or gouges. If there are no unusual marks on the bolt Id try putting just the bolt into the barrel extension with no carrier. The bolt should easily fit into the barrel extension. See if there is much resistance in rotating the bolt in the barrel extension. If the bolt isnt binding in the barrel extension then Id check to ensure the mag is not interfering with the carrier.
If everything looks ok it sounds like you are not getting enough gas. You could try to open the gas block completely to see if the spent casing ejects. Look at the spent brass and make sure it looks ok. Some times a rough chamber will show up on the brass. Your using quality components so unless you have a rough chamber the only other component is the buffer spring and buffer.
Id measure the buffer spring and weigh the buffer. Make sure you are either using carbine buffer tube with carbine buffer and spring. If using a rifle buffer tube use a rifle length spring and rifle buffer.
One other thing to check is the cam pin is not out of spec, moves properly and has no unusual wear marks.
If everything looks ok it sounds like you are not getting enough gas. You could try to open the gas block completely to see if the spent casing ejects. Look at the spent brass and make sure it looks ok. Some times a rough chamber will show up on the brass. Your using quality components so unless you have a rough chamber the only other component is the buffer spring and buffer.
Id measure the buffer spring and weigh the buffer. Make sure you are either using carbine buffer tube with carbine buffer and spring. If using a rifle buffer tube use a rifle length spring and rifle buffer.
One other thing to check is the cam pin is not out of spec, moves properly and has no unusual wear marks.