AR 15 Guru question.

[Shovelhead]

Man the plot thickins.
We can rule out the 223 Barrel in works anywhere.

Now the thick part..

I have now two NiBx BCG's from two sources CORE 15 and AR Stoner (MidwayUsa)
I have two NONE NiBx BCG's from two sources PSA and JoeBob's

The 300 BO barrel in either upper works fine with either NONE NiBx BCG's (PSA or JoeBob's)

Yes... 300 BO barrel with NiBx BCG's will not seat the BCG in either upper.
When you typically insert the Charging handle slide in the BCG and move into the upper you
reach a point maybe 1/4" an you usually just thumb press and the BCG/Charge handle "Snap"
fully inserted and you can mate the upper to a lower.

With these two NiBx BCG I get to that 1/4 " stop and no manner of hand/thumb pressure
can push until it seats.

Again keep in mind the 223 barrel works fine with ALL BCG's in both uppers any combination.

Bottomline the 300BO barrel fails to work with NiBx BCG of two different sources.

 

[DinkyDau]

Take close ups of the Upper bare on the open side. Close to the forward assist..DD

 

[Shovelhead]

Take close ups of the Upper bare on the open side. Close to the forward assist..DD

DD photos of each upper is that what you would like to see?

 

[b.a.customkydex]

I think you've got a tolerance stacking issue with the NIB bolt. There's only a few thousandths of clearance inside the barrel extension. If the NiB bolt lugs are too long or the depth of the extension is too short, the bolt may be binding up and unable to lock.

Ding ding ding I think we have a winner

 

[DinkyDau]

May have read this wrong, Had a problem back a few year ago with an upper, It would not mate with a good lower. The lower worked on several other uppers..I found the problem..Used Bearing wax to narrow it down..It was a problem with the upper that I solved with some JB Bore compound and a lot of elbow grease..DD

 

[Shovelhead]

Could it be the M4 cuts look at the BO barrel on left the 223 on the right???

 

[Shovelhead]

Originally Posted by mtdawg169
I think you've got a tolerance stacking issue with the NIB bolt. There's only a few thousandths of clearance inside the barrel extension. If the NiB bolt lugs are too long or the depth of the extension is too short, the bolt may be binding up and unable to lock.

Ding ding ding I think we have a winner

If I take the BCG without the UPPER will that be a good test? OK it's two BCG's so I'suspecking the 300BO which
by the way is the second one I recieved because we thought the 1st one was the culprit.

 

[CBeck]

So worst case scenerio you can still use the non NiBx BCG with the 300 BLK and the NiBx BCG in the .223 and still have two complete functional uppers. Not all bad.

 

[AR Trader]

Does the head of the NiBx bolt fit all the way into the barrel extension when neither are mounted in the receiver?

 

[b.a.customkydex]

If I take the BCG without the UPPER will that be a good test?

That would be my next try...see if the bolt will lock up with the barrel out.

Are you running a billet upper with a Seekins rail?