By the time of the stat of the Revolutionary War the 13 colonies had a highly developed iron industry. If taken as a single country they were in the top five iron producers in the world (some say third in terms of exports). Those in the antique gun world who have mentioned iron being scarce or expensive have not studied the period documentation.

One of many source documents would be the Customs Report for exports to London and other British ports from the colonies. These survive for most years from 1707 until 1776. The records of Virginia and Maryland are lumped together (PA is separate but I have not studied those records). Here are a few examples of the exports from VA and MD to London [weights are British long tons of 2200 lbs.]:
In 1770 — 512 tons of bar iron (wrought) at 9 ½ to 10 ½ pounds (value) per ton and 1125 tons of pig (cast iron) at 18 to 20 shillings per ton.
1771 —654 tons of bar at 9 – 11 pounds and 1857 tons of pig at 18 to 20 shillings per ton.
1772 —344 tons of bar and 1309 tons of pig (same prices)

The Brits were buying both bar iron and pig iron from the colonies, manufacturing it into finished goods and selling those back to the colonies, literally, by the boat load. The Iron Act of 1750 had been written to encourage the American manufacture of more pig iron and bar iron and restrict the production of plate, sheet and nail rod. It has been considered by some historians to be the first of those intrusive acts that lead to the Rev War but that is, as they say, a whole other story.

The Iron Act of 1750 is probably the source of persistent myth that it was "illegal" to manufacture iron in the colonies prior to the Revolution. The act did prohibit the building of any more rolling and slitting mills but even this was ignored and considered unenforceable. (top)

CAST IRON, WROUGHT IRON and STEEL

There were three types of ferrous metal in use in the Colonial period: cast iron (high in carbon and brittle but excellent for making items like frying pans, Dutch ovens, cannon balls and the cheaper grades of cannon); wrought iron (low in carbon and very tough so excellent for anchor chains, nails and musket barrels) and steel (carefully controlled amounts of carbon allowed steel to be hardened for specific uses such as knife blades, files, saws, springs, musket ramrods and swords).

CAST IRON
Cast iron was produced at a blast furnace. Iron ore, flux (limestone or oyster shells) and charcoal were loaded into the top of a furnace usually made in the form of a flat topped stone pyramid. Air blasted into the furnace caused the fire's temperature to approach 2000 degrees, freeing the iron from the oxygen and other minerals in the ore. It was common to fire a furnace for days on end without letting it cool down. At intervals liquid iron was drawn off from the bottom of the furnace. The liquid iron flowed in channels made in the sand floor in front of the furnace. Most of the iron was cast into ingots called "pigs" These came in different sizes and the bigger ones were actually called "sows" because the smaller pigs seemed to be nursing on the larger sow. Furnaces could also cast objects like cannon balls, cannon and Dutch ovens by ladling iron into sand moulds as a foundry operation.

The liquid iron was in direct contact with the burning charcoal and that caused it to be high in carbon (4-5%). Huge amounts of charcoal were required and it took literally thousands of acres to make the charcoal for a single furnace. (top)

WROUGHT IRON
There were two different ways to make wrought iron (with many variations of each).

Wrought iron can be made directly from iron ore. The ore is heated in a small furnace called a bloomery but it is not completely melted. Instead a spongy mass called a "bloom" is extracted from the fire and forged, in a process similar to kneading bread dough, until most of the impurities are removed. Because it was never liquid the iron did not absorb much carbon and what was there burned away during the repeated welding. Colonial Williamsburg's Anderson Blacksmith Shop experiments with making iron in a bloomery. 2008

Wrought iron can also be made from cast (pig) iron. The pigs are re-melted on a shallow sand lined bowl by a blast of flame. The molten iron is stirred and the blast burns away the carbon as it is exposed on the surface. As the carbon content drops the melting temperature rises until the mass is no longer liquid. The resulting bloom is then forged into bars with large water powered trip hammers.  The more the bar is folded and welded back on itself the more highly refined the iron becomes. The "grain" of the iron becomes finer as the silica inclusions become smaller and smaller.

A bar of wrought iron that has been cut part way through then broken to reveal the "grain."

Wagon wheels, anchors' and such were made of lower quality iron but gun barrels, lock parts (not counting the springs) and mounts were usually made of very high quality wrought iron. More refinement under the hammer produces higher quality which translates to finer grain.

Salt water etched the wrought iron revealing a very course grain in this anchor.

Note that the grain in the iron of the reinforcing cross bars is perpendicular to that of the link. The bars were separate pieces welded in place.

Holes such as this were much easier to hot punch than to drill.

Wrought iron objects could be surface hardened or “case hardened” by heating for a fairly short time in the presence of carbon and that is how the lock parts, other than the springs, were heat treated. That is forged, filed, and polished in soft iron, then case hardened for wear resistance. Depending on the temperature and the amount time the iron is in the carbon pack, the case hardening can penetrate deep enough to convert thin cross sections, such as the nose of a sear, completely to high carbon steel. (top)

STEEL
Here is the definition of steel in Samuel Johnson's 1755 Dictionary: "Steel is a kind of iron, refined and purified by the fire with other ingredients, which renders it white, and its grain closer and finer
than common iron. Steel, of all other metals, is that susceptible of the greatest degree of hardness, when well tempered; whence its great use in the making of tools and instruments of all kinds.” "Steel is made from the purest and softest iron, by keeping it
red-hot, stratified with coal-dust and wood-ashes, or other substances that abound in phlogiston, for several hours in a close furnace.”

Thin strips of highly refined wrought iron were layered ("stratified") with charcoal (often a mix of bone, leather and wood charcoal) in a box that could be sealed to keep air out. The box is heated to about 1500 degrees and kept hot for many hours. The carbon soaks into the iron and converts it to steel. The name "Blister steel" comes from the blistered blue-gray scale that forms on the surface of the bars. Blister steel was imported mostly from England and Germany and available in many colonial stores. Due to the long soak the carbon is distributed fairly uniformly but there would be a bit more toward the outside of the bar.

For some applications where uniformity of carbon content was very important, blister steel could be further refined by bundling strips together, forge welding them into a mass and then drawing this back out into a strip. That could be repeated several times but that was done only for the best cutlery, razors and clock and watch springs. Because of the intended use this more uniform steel was called "shear steel."

In about 1739 an English watchmaker, Benjamin Huntsman, discovered that under the right conditions blister steel could be melted in a crucible and stirred while liquid. This caused very uniform distribution of the carbon. Steel made this way was called “cast steel.” By the late 18th century "cast steel" was being used for cutlery and chisels. Contrary to popular belief a chisel marked "Cast Steel" was not cast! It was forged from a bar of steel that had been made through the crucible process. (In the early 19th century some rifle barrels were made of cast steel but most were wrought iron until after the Bessemer process made uniform, high-quality steel much cheaper in the mid-19th century.)

Many objects were made of a combination of wrought iron and the more expensive steel. Axe heads of wrought iron had a steel bit that did the cutting. Likewise wood chisels and plane blades had a layer of steel welded on the side that formed the cutting edge. (top)