There is a good deal of discussion about this all over the place, and it’s pretty important where it comes to firearms.

Predominantly, there’s a simple way to explain it all: A forged bar is like a board, and a cast bar is like a piece of particleboard. Particleboard shelves are fine if you’re going to be using them for pictures and knickknacks, even paperback books if the span isn’t too far. But if you’re going to keep glossy books on the shelf, you want the board.

It is the grain of the board that is critical in this example; the regular board cut from a tree has layers and layers of aligned cells that are deposited as rings as the tree grows. When the tree is cut into boards, the sawyer tries to make the grain as straight and true as possible. Particleboard, on the other hand, is made from compacted sawdust- some, even without any binders, a combination of heat and the resins inherent in the sawdust cause the binding together of the individual grains of sawdust. The bonds between the grains of sawdust are small and weak, and even though it holds together for normal furniture, it’s the laminar structure of the natural wood that gives strength.

That word is extremely important to the rest of this discussion: Laminar. It means “Flat” or “Straight”. It is what gives wood it’s strength on a cellular level, and what makes plywood strong- in fact, the different layers in plywood are called “Laminations”.

Particleboard has been “Improved” though the years, and now they make a product called “Aspenite” or “OSB”(Oriented strand board) which combines some of the properties of more expensive plywood with less expensive particleboard. Strands of Aspen are aligned and then bonded and pressed together under heat and some not inconsiderable pressure, resulting in a product that has found a common home in home building and repair projects. Hardly a garden shed exists that doesn’t have a couple sheets of aspenite in it.

There are several properties of metals that are critical to how it is used. In no particular order:

Elasticity is the property of metal wherin it can “Spring back”, the ability of a metal to be deformed up to a certain point and return to it’s original position, and do so for extended periods of time. Watch springs, car springs, all springs are examples of metals that have a high level of elasticity.

Ductility is the property of a metal that allows itself to be elongated or stretched. Ductile metals include copper and certain alloys of aluminum, that can be drawn into wire quite readily.

Malleability is the ability of a metal to take on a shape via compression without rupturing. This may sound complex, but think of bread dough and cookie dough, for a moment. Bread dough can be rolled out quite thin, but if you mash a wad of cookie dough it cracks around the edges (Usually) because it is not malleable. By the same token, certain alloys of certain metals will fracture at the edges if beaten enough. Look at an abused wood splitting wedge, for instance, or a cold chisel that has been repeatedly hit by a hard faced hammer. Malleability is what allows gold to be hammered- using the crudest of methods- into sheets that are only a few molecules thick.

Toughness is defined as the ability of a metal to resist penetration. A tough metal may be used for it’s properties of impact absorption, as in the crush zones on modern cars. Most of them are made from metals that can permanently deform but not fail. There’s an impact absorbing pipe in the steering wheel of your car; otherwise you’d have a hole punched in your chest if you got in an accident. Same with the front bumper, since the 70’s. The pipe or metal bracket crumples instead of translating the inertia to the occupants of the vehicle. Another example of tough metal is the guard rails on the edge of the highway- they are made to self destruct while absorbing the impact yet prevent the vehicle from plummeting off the edge of the road.

Brittleness is the tendency of a metal diametrically opposite plasticity. Hard tool steels can be very brittle, as can cast iron and steel, but brittleness is not the same as hardness; cast iron can be so soft it can be carved easily with a pocketknife, but carbide will cut almost anything and shatters quite as readily as glass.

There are a lot more pieces to this puzzle, and we are still learning what some metals can do. We do, however, have an extraordinary body of knowledge about things just because we have been playing with metals for (relatively) so long.

One of the things we discovered quite readily about metals was this: They don’t always have the same properties. Sometimes, when you warm something, a metal that is ordinarily brittle becomes malleable. Sometimes you can change the hardness of a material by heating it and then cooling it, and sometimes you can change the other properties as well, by adding other elements to the iron.

Iron and steel do not have “Molecules” in the same way we think of other things having “Molecules”. Iron and steel form a crystal lattice with particles of iron, carbon, and other elements. When strain is placed on those crystal lattices by outside forces, the resulting bonds can act in unusual manners. One such instance is heat; under the correct conditions, enough heat applied to steel causes it to lose it’s abilities to react to a magnetic field. On cooling, the steel reverts to it’s former magnetic properties.

Using heat and forging allowed early metalsmiths to use inferior, impure steel to make superior weapons, by any number of methods, predominantly by heating and drawing the iron until it made the shape you needed, either for a sword or a plowshare or whatever you needed.
Early on, the swordmakers of Japan, and later Damascus and Toledo, figured out that they could enhance that “Drawing” process by folding the metals used and then drawing them again and again. This made for some really amazing steel, and though the swordsmiths didn’t understand what they were doing, exactly, at least at the molecular level, they understood well enough to do amazing things with the steel.

See, they were able to change the crystalline structure of the steel by “Squooshing” the atoms of steel and carbon and etc together in ways they would not have assembled themselves naturally.

When you make a cake, you assemble ingredients, and sometimes those ingredients form chemical bonds together that make them form new substances. Baking powder and water, for instance, produce carbon dioxide, and leaven the cake (or bread, or whatever) but for the most part, there is no physical action you can do to a cake that will dramatically improve it’s comestibility. Metals, when they are alloyed, are still composed of the same ingredients, but in tiny amounts, in the crystal lattice. Hammering the steel, unlike hammering the cake, has an effect on that structure, and the effect can be very good indeed.

Because that crystalline structure is similar to the cells in a piece of wood, it can be said to have a “grain” And forging causes that “grain” to move in a very specific way.

Imagine a simple chair made out of particleboard. It wouldn’t be very strong- the legs, simply under compression, might be OK, but the seat wouldn’t have much strength, and a guy my size would invariably end up on the ground. Making the chair out of boards helps and works fine, but eventually, even the best constructed joints come loose.

Boatbuilders at one time would search for trees with “Knees”, bends that allowed them to make the keel of ships out of one unspliced piece of wood, for maximum strength. Imagine being able to make a chair out of one piece of wood, grown in the shape of a chair, simply waiting for someone to come along and scrape off the bark. It would be immensely strong, because the ‘grain” of the wood would be unbroken- it would transition smoothly around bends and corners and the unbroken strength of the grain would be almost impossible to separate.

This is what forging does. Forging allows you to do just that; to make the grain of metal flow in a laminar method so that the grain takes on the shape of the part that it is required.

There are a few issues there. It’s very possible to forge a crankshaft or a connecting rod and have the flow of the metal be very near to the actual finished size and shape. On the other hand, forgings of complex parts can be a real pain in the ass.

The thing that makes forging work so well for some parts is what is called ‘Near net”. Near net means that the part is forged to as closely as possible to the final shape of the part- some parts are forged so close to the final shape that only the critical surfaces are machined at all. Pistons, connecting rods, crank and camshafts, all show at least half their surface as forged, not machined at all. What this means is that the grain follows the actual shape of the metal, and keeps it extremely strong.

On something like a 1911 slide, it is impossible to practically forge a part to near net, at least on the inside where it is critical. All those surfaces are machined in some way. So the advantages (in that respect) provided by forging are not really dramatically better than machining a slide out of a bar. Forging technology is improving all the time, of course, so the likelihood that a near net 1911 slide forging is in our future is probably good.

Forging does have other properties that do help that slide, though, and make it superior to cast or billet machined slides. The grain of a forging, while it doesn’t follow the contours of the inside of the slide, does follow the length of the slide, making it extremely strong in that direction, making it much less likely to stretch and change headspace. Forging also allows the secondary heat treating of the part to result in more uniform properties.

All metals are a combination of the above properties in various percentages- you want hardness to resist wear, you want the resilient ductility, and the toughness to resist the forces that the item will encounter.

One of the parts that is often forged to near net is the AR receiver. The amount of machining that gets done to these is minimal, for several reasons. First, because the less machining required the mess expensive they are to make, and second, the less material is removed, the stronger the aluminum is because the “grain” of the aluminum is flowing directly in the direction of the stresses in the metal.

It is not lost on most of the people I know, that are aware of how metallurgy works, that the “Reardon metal” of Atlas Shrugs is not only a physical impossibility, but a laughable stupidity.

The science of metallurgy is pretty well fixed and known, and only being able to smelt materials in zero G will ever allow us to move beyond our current level of ability, I expect. While we learn interesting and new things from time to time, those times are fewer and further between with each new step.