I got that but they are not the same as the post 72 AR’s at all. They changed the internal parts and pin locations so that the select fire and the semi auto parts can not be interchanged between receivers.
There has never been an AR sold on the civilian market that I know of that is select fire. Very few of them were sold that the parts would interchange either.
I don't think that is totally true. I usually don't like giving libs info about this on open forums but many can be made to be select fire. It takes some work. Basically these steps are made... you change to a M-16 hammer that has a notch to engage the sear or drop in auto-sear that is also to be installed. Also ensure the lower can accept the auto sear to be fitted. And change out the select-fire switch (safety detent) from the straight semi-auto version one to the one that has a notch in it.
You may also have to change out the bolt carrier if you have a Colt AR15 since they installed ones that would not work to trip the auto-sear. However, many companies already install the M-16 type bolt carrier assembly. A competent gunsmith could make AR-15s to select fire.
There has never been an AR sold on the civilian market that I know of that is select fire. Very few of them were sold that the parts would interchange either.
If it was made before 1986 you could buy an AR15/M16 full auto version. They sell for a premium price, and you pay the $200 tax and wait for a long background check, which they stretch out.