Some receivers for the Rifle, Automatic, Browning, Caliber .30, M1918 and M1918A2 were cast....cast iron to boot.
In aluminium is a big difference but is there any big difference in steel ?
If you look at the physical properties of aluminum alloys, they are divided into two classes, wrought alloys and cast alloys, and alloys with the same chemical composition have different physical properties. However, if you look up steel alloys, you will note that only the chemical composition differentiates alloys, for instance, there is no listing for wrought 8620 steel and cast 8620, like there is for aluminum.
That is because the difference between cast steel alloys and wrought alloys (forged or rolled) are much less that that of aluminum and far more dependent on other factors.
The added benefit of forging is the realignment of the grain structure, and just because someone dropped a twenty ton hammer on a block of steel does not automatically means the grain structure is magically better. It is better only if the grain structure is arranged correctly.
Let's take an extreme example, suppose you drop a hammer on a block of steel 6.25 inches long, 3.25 inches wide and 3.25 inches deep and forged it into a rectangular block that was 6 x 3 x 3 inches with a lot of flash. Would that be appreciably tougher than a cast block of the same dimensions?
No, it wouldn't. Because you have not altered the grain structure.
Look at the receiver forging Springfield, Winchester and H&R used in the original M14s:
Note how the area of the locking buttresses has been formed, meaning the grain structure now follows (roughly) the external contours. This is how toughness was added.
Compare that to this commercial forging blank:
This forging is only a very slight improvement over a casting, because the grain structure around the all important locking buttresses has not been altered significantly.
Also, you only get moderate increases in strength through forging, what you get is increases in toughness and fatigue resistance. For an M14 receiver, with the size and shape of the locking buttresses, and the actual loads, neither of these are major concerns. With the bolt, however, these factors are much more important due to the higher bending stresses on the lugs. So, a cast receiver is more than adequate, but a forged bolt is very important.
And what goes for the bolt also goes for the operating rod, that weird bend at the transition from the tube to the external part has some high stresses.
