I'm almost done with my second build but I have a quick question before I finish the job. The barrel alignment pin is not touching the back of the upper receiver. (see pictures below)
Is this a problem? I torque it twice to 32 lbs and removed the nut, it has not moved back at all. This is a used Bushmaster A1 upper and an unknown 11.5 with a 5.5 barrel which is only marked "5.56". The previous owner of the barrel said it had a headspace issue, it would close on a no-go gauge. Could an oversize barrel pin have caused that along with the "horrible accuracy" he experienced with it?


I can't remember if this is right or not. I remember my first build and the post that followed. "Boy did I F' this up"

You're OK.  The pin is just for alignment, and really doesn't have to seat to the rear.

Headspace is a chamber bolt relationship, so the alignment pin has nothing to do with that.

If it measures with long headspace, I'd proceed slowly and with caution.  You never know what could happen.  I'd be hesitant to use this barrel, myself, knowing it had so many previous issues.

Quoted: You're OK.  The pin is just for alignment, and really doesn't have to seat to the rear. Headspace is a chamber bolt relationship, so the alignment pin has nothing to do with that. .

Am I off in thinking that the chamber could be a little far forward with the barrel? If the pin/barrel moved back a bit more would this cure any possible head space issue?
BTW: The previous owner had an old bolt when he checked head space which might have also been a factor?

Quoted: Quoted: You're OK.  The pin is just for alignment, and really doesn't have to seat to the rear. Headspace is a chamber bolt relationship, so the alignment pin has nothing to do with that. . Am I off in thinking that the chamber could be a little far forward with the barrel? If the pin/barrel moved back a bit more would this cure any possible head space issue? BTW: The previous owner had an old bolt when he checked head space which might have also been a factor?

The pin and chamber really don't have a relationship.  The pin is simply there for alignment.  Headspace is the relationship between the chamber and the bolt.  The barrel extension plays into this, but the pin is just a pin and cannot affect this relationship.

An old bolt can extend headspace a little bit.  

OK, I get it now.
I'll check my first few rounds of brass carefully.
Norinco has the weakest brass right? Figure if it runs without problems on Norinco it should be good to go.