New LH AR build - seeking advice

[B!ngo]

So I am about to embark on a new AR build and need some advice. I have all of the parts and pieces but have a question about one rather obscure issue.
I'm building a left-handed design starting with a Stag lower and upper stripped receiver, a DD 14.5" barrel and an appropriate muzzle device to ensure it meets the legal length limit. No big issue so far.
My confusion is regarding the barrel extension (at the receiver end). I purchased from Brownell an ambi barrel extension with the understanding that I would have to have my FFL replace the existing barrel extension with the ambi part. I spoke to my gunsmith (whom I will need to help pin the muzzle device to the other end of the barrel) and he said it's not necessary. He's never seen one nor heard the need for one in a left-handed build.
Does anyone have an informed opinion?
Thx,
B

 

[briansmithwins]

1) The barrel extension is symmetrical. There is no right and left handed version.
2) You don't replace a barrel extension unless you're finish reaming the chamber. The extension is installed, the chamber reamed, bore plated (optional) and gas port drilled. You can't replace a extension because that part determines headspace and can't be adjusted.

BSW

 

[B!ngo]

Thanks. And yes, I was aware that I could not replace the extension myself but that it would have to be done by a gunsmith because of all of the things you cite. But there is a subtle difference between the extension on the barrel and the one that I purchased that was marked as 'ambi'. The change is that there is a bevel on both sides of the bottom 'teeth' of the extension on the ambi one while there is a bevel on only the right side of the 'teeth' of the one on the barrel. Or so it seems.
To be clear, I don't want to have to deal with this extension thing. The cost of the new one I purchased was minimal so it's no great loss if I don't use it. I just wanted to be sure that the gun will feed and eject properly once assembled.
B

 

[briansmithwins]

That does not sound right. Can you post a pic?

BSW