Out of spec carrier?

[Mister Ridge]

Helped someone I know rebuild an upper recently. Took a Spike's 16" 5.56 upper apart to rebarrel it with a Shilen 6.5G barrel. The 5.56 had never been fired by the owner but appeared to have been test fired and cycled fine. After installing the Shilen barrel, it became difficult to cycle and would stick closed, requiring tapping the charging handle with something to get it to come back.

Tried more lube, since it seemed a bit dry. Didn't help. Tried swapping to a different charging handle, which also didn't help. Took the bolt out of the carrier and it still stuck forward. Also noticed that the barrel protruded further into the receiver than another 5.56 upper that was on hand.

I ended up swapping just the carrier between the two uppers on hand. The 6.5G now cycles easily, while the 5.56 is a bit difficult but doesn't lock up like the 6.5 did. Out of spec carrier? Tolerance stacking? Sticking on the gas tube? No time to test fire either right now.

 

[LRRPF52]

Took the bolt out of the carrier and it still stuck forward. Also noticed that the barrel protruded further into the receiver than another 5.56 upper that was on hand.

Would need to see comparison pics between these 2 because that’s basically unheard of.

Are you saying the barrel extension is seated back further and visibly so inside the upper, when looked at from below the separated upper?

 

[Mister Ridge]

Would need to see comparison pics between these 2 because that’s basically unheard of.

Are you saying the barrel extension is seated back further and visibly so inside the upper, when looked at from below the separated upper?

That's what it looked like.

 

[greentick]

...Also noticed that the barrel protruded further into the receiver than another 5.56 upper that was on hand.
..

Either the extension is out of spec or the the receiver or both if it is deeper into the receiver?

Extension is too long?

Or, someone "squared" shorter receiver too much?

Tagging in to see how this works out, keep us posted. Always learning.

 

[Ravenworks]

Flip the upper over and take a picture of the gas tube as it sits in the relief.

 

[Mister Ridge]

Flip the upper over and take a picture of the gas tube as it sits in the relief.

Like this?

 

[Mister Ridge]

5.56

6.5 Grendel

It should be reiterated that the Grendel now cycles fine after switching just tje carrier. The carrier that was sticking in the Grendel cycles okay in the 5.56 but sticks a little.

 

[steve101610]

I had this issue before and the cause was the gas key was not bored out enough and was basically pressing the gas tube into the gas key. Drilled out the gas key to spec and everything worked fine after that

 

[Ravenworks]

Your gas tube looks to be long, it should be centered in the cam pin cutout