A friend of mine sent me a AR-180B upper receiver to look at and study. Here are a series of pictures giving you a more detailed look at it.
This is a right side view. As you can see they were made with out a dust collector flap.
A shot of the under side showing the welded seam.
Close up of the rear sight stamping.
A close up of the tig welded area for the front trunnion.
This is a series of pictures showing the front of the trunnion
A couple of shots of the bottom of the trunion
Well this is exciting! Waiting impatiently for the AR16… Very impatiently.
My research indicates that the AR15 barrel extension was turned down, pressed into the trunion, then pined in place before being be welded into the upper. I have been unable to determine if the pinning part is accurate or not but I do know that if you do not use a reaction wrench to hold the extension when removing the barrel and simply clamp the flats of the receiver, the extension will turn inside the trunion. Without drawings or a 180B trunion by itself, we may never know for sure. Maybe there is a demilled upper floating around somewhere.
They were not pinned.
I am not sure that the AR-15 trunnion was even turn down. I am working on solid models of the two parts to determine if that is the case or not.
Would this lower receiver fit a original Armalite AR-18 and make it semi auto instead of full auto?
It should fit an original receiver it does not have the capability to install a trip sear that would be required for a full auto. This is a semi auto upper receiver only.