I have parts for a build, a custom barrel and everything.  I was thinking about changing plans and using a left hand ejecting upper in stead.  I never had a problem w/ right hand ejection, but you get a lot less gas in the face when your face isnt' on the same side as the ejection port, particurlarly if you are shooting suppressed.  

I understand that normally a barrel ext is installed and headspaced, then the gas port is drilled and if you replace the BE it might not time the same and then your gas port would be in the wrong place.  

is there a way to eitehr champeher the BE lugs w/ it in stalled or to remove it, champher it, and reinstall the same BE or is it done for one you drill out the pin?  

thx

I didn't think there was a difference in the barrel extension between right hand and left hand rifles? Just the BCG and upper receiver are different I believe

the part is the same except that they champher the opposite set of lug edges on the BE and bolts for left hand guns as the bolt also rotates the different direction.

Chamfer

thx

I did not know they altered the barrel extension for left hand rifles. I have now built 2 left handed uppers and used regular barrels and extension and so far they run flawlessly and both are very accurate. So maybe I got lucky (twice) or it doesn't matter.

Never heard of any difference on barrel assembly.  Never seen a barrel being sold as a "left handed barrel".  It's a straight tube, and fits into an upper receiver.

the AR is spec'd to have one side of the BE lugs chamfered so there is less chance of sharp edges getting caught on eachother.  It may be of little import.  when people build barrels for LH use, i mean when they install the BE, the do this.  this is becausr the bolt rotates in thhe opposite direction.  

i suppose in "adverse" conditions it may help ensure the gun goes into battery.  In a typical generous milspec headspace i am not surprised that left hand bolts usuallly run in R hand rifles.

They make an ambi barrel extension. As you started to describe, it the locking lugs have both sides of the leading edge chamfered to minimize wear on the bolt lugs. A standard barrel extension (right handed for the sake of this conversation) only has one side chamfered. A left handed bolt (at least on the Stag Arms type setup) enters the barrel extension and rotates the opposite way as a right hand or standard bolt would. When you fire and it ejects, if the bolt is riding across a standard extension there's a sharp edge instead of a chamfered one.

Many people run left handed bolts on a standard extension and never have issues. I fully believe it's better to have an ambi extension and that it will decrease wear on the bolt. I don't see how you would be able to add this chamfering to an existing extension. It's on the inside of the lug, and even with the barrel off that would be a very tight area to work in.

Another factor to consider... When the gas from the gas tube goes into the carrier key, it's pushing the carrier backwards but the bolt forwards. There's a tremendous amount of pressure on the locking lugs upon firing. The gas entering the chamber of the bolt carrier group helps to equalize this pressure to allow the bolt to unlock.

Bottom line - If I was buying all new parts I'd definitely hunt down an ambi extension. However, if you already have a setup I don't think I'd risk effing up a barrel to add that chamfering. Were I you, I'd buy one or two spare LH bolts for your carrier and shoot the piss out of whatever barrel you already have. Keep it well lubed and I doubt you'll ever have an issue.

thx sir

ok, so with the stag the bolt rotates in the opposite direction and so therefore a proprietary bolt carrier is required. However I discovered that the DPMS also had their South paw. It just uses a slick side upper. But it uses the standard bolt carrier and the bolt rotates and the normal directions. It just has the extractor on the other side of the bolt. Therefore that should work fine with my standard barrel extension.

seeing your post again i wonder if you know how the barrel, barrel and upper reciever all fit together...