Gunsmithing AR-15/M4 barrel extension swap

[animalmother85]

I have an AR-15 I've been putting together over the past two deployments, it's a 24" barreled 6.5 Grendel. I bought the Upper receiver and the barrel at the same time from two different vendors. I assumed the barrel would come with M4 feedramps in the barrel extension, so I ordered the upper for that. Turns out, my barrel extension doesn't have them. I went through with the "dremel" idea, it works but I'm not particularly happy with it. I want to switch the barrel extension for one with M4 feed ramps cut into it from the get-go. I understand that I need the barrel extension removal tool, as well as the little pin that aligns the upper with the barrel. I have a head space go and no-go gauge ready to be ordered as well. The barrel has less then 100 rounds through it, so I don't think wear would be an issue, but I want the gauges to make sure. I gather the torque spec is anywhere from 35-80lbs on the extension. What else do I need to do? I want to do this right and do this once.

 

[Oodin]

Re: AR-15/M4 barrel extension swap

I think you would have/want to make sure the extension was timed properly so that the gas port is pointing straight up when the extension is installed.

Not sure how to do this, just that should probably be done.

 

[Outsydlooknin75]

Re: AR-15/M4 barrel extension swap

In all honesty, either shoot the piss out of it the way it is now ....... OR buy a new barrel with the extention installed and M4 cuts.

I dont understand why people think that the m4cuts are necessary, but they seem to think they are.

Swapping extentions isnt as easy as it sounds and really should be done by a professional.

 

[smokshwn]

Re: AR-15/M4 barrel extension swap

If you are unable to time the extension properly to line up with the existing gas port then I would either replace the whole barrel or send it to a smith who can do it correctly. This job is more than tools and a vice for the home gunsmith.

 

[GasLight]

Re: AR-15/M4 barrel extension swap

since the barrel already has the hole drilled to press the pin into, that pin is already lined up with the gas port. The problem will be making sure the extension will time right to that pin hole. The other problem, is if the extension will allow the bolt to headspace to the barrel properly when you get the extension to time properly to that hole. As stated above, this is likely a job for a 'smith unless by some amazing alignment of the stars, you get an extension that properly aligns and headspaces at the proper torque without any metal removal.

DD