The "cold" hammer forged barrel is done on a rotohammer, it swages the barrel around a mandrel which produces a finished barrel. It is quite accurate.
The "hot" forged receiver is done on a drop forge with a very large weight and several molds, the hot ingot is placed inside a mold, the weight or hammer is dropped, the weight smacks the blank and shapes it to the mold. During the War military manufacturers had a number like 7 drops to complete the forging. Hot forged does not make a complete finished part, it makes it into an outside correct shape with the inside still full of metal, the machining process removes all of the inside metal, they do a finish machine on the outside with flange removal. The barrel process is completely different than the receiver.
There has been some great debates as to the correctness of current or past civilian receivers being manufactured to USGI prints. The general consensus in my opinion; there has never been nor are there any that have been made to USGI prints. The fact the M14 was full auto and the M1A is semi required dimension changes, on the op rod ledge, it got wider, the rear of receiver got thicker, dismount notch got moved and so on. This caused the design prints to be modified, which means the manufacturer, depending on who that was, changed the dimensions to meet their needs both for the semi conversion as well as their machining requirements. No current manufacturer has the capability to replicate the machining done on the originals.
Having said all this, it really depends on what you want, some want name recognition, others feel strongly about buying "American only", others believe cast is as good as forged or vice versa. You have to decide what is important to you. All receivers made by every manufacturer has good ones, everyone also has suspect ones. Everyone here will have good cause to explain why they have what they have.
Buy one , build one, I guarantee one will not be enough.
Jim