Molten metal was the ultimate judge of load-bearing truth. In the fire crucible, bad math and lazy metalworking didn’t hide. They rusted, segregated, and exploded.
Midnight in the Grey Crag foundry smelled of burning hard coal, sulfur, and glowing charcoal.
The central blast fire was roaring with an ear-splitting, throaty rumble that shook the bedrock floor. Two massive leather bellows, driven by a crank-shaft connected to the grist mill water race, pumped blasts of pre-heated air through the baked-clay tuyeres at four pounds of pressure.
Master Borin Bronze-Lung stood on the charging platform, surrounded by glowing sparks.
He wore an apron of double-thick bull-hide, long iron gauntlets that reached his elbows. His signed name dual-sky-slit sight disappearing-filament fire gauge hung from a leather strap around his neck.
Borin lifted the brass instrument to his eyes, squinting through the twin smoked-glass lenses into the fire check port.
Inside, the molten charge was a blinding, blazing bright white-orange sea.
“Filament matching current at two thousand two hundred and forty degrees Fahrenheit,” Borin called over the fire roar, chanting the heat like an ancient dwarven battle song. “The copper has run liquid as spring beer. The pig-iron master alloy is dissolving into the melt.”
Giles Croft stood on the casting floor with his drafting clipboard and a long iron skimming rod.
“Maintain heat for twelve minutes,” Giles instructed. “The iron needs complete heat diffusion into the copper-tin matrix. If you pour before dendritic homogenization is complete, the iron precipitates into brittle nodules that ruin the bore.”
“Aye, Lord Giles,” Borin barked. “Let the iron drink the copper. Hold the draft steady, boys.”
Beside the fire pit, Toby Karr and four apprentice foundrymen stood with long iron skimmers. Their young faces glowed cherry-red in the fire glare.
In the center of the sand pit sat the two upright molds.
They were massive cylinders of baked heat-proof loam. They were bound in heavy wrought-iron hoops and buried up to their rims in dry river sand to resist water-pressure liquid head pressure.
Down the center of each mold hung a hollow iron core-pipe wrapped in combustible straw rope. Cold water from the aqueduct water chute was piped through the iron cores. It drained out the bottom into a gravel ditch.
“Core cooling water flowing at six gallons per minute,” Toby reported, checking the discharge pipe. “The iron cores are cool to the touch.”
“Check the risers,” Giles ordered. “We need adequate feeder head volume to compensate for liquid-to-solid volume shrinkage.”
Master Duncan Stone-Splitter stepped up with a long iron ladle, his heavy leather mittens coated in lime. “Feeders are topped with charcoal dust, my lord. The gates are clear.”
Giles checked his pocket watch.
The second hand ticked through the twelfth minute.
“Skim the waste scum,” Giles commanded. “Prepare to tap.”
Borin stepped to the fire spout with a long steel tapping bar. He set the chisel point against the baked fireclay plug at the base of the hearth.
He swung an eight-pound sledge.
The fireclay plug shattered.
A blinding, roaring river of molten bronze-iron alloy erupted from the hearth spout.
The white-hot metal hissed as it cascaded down the heat-proof clay runner trough, throwing showers of golden sparks across the foundry ceiling.
Toby and Duncan right away dipped their skimmers into the liquid stream, raking away the frothy, glowing melted rock waste of copper oxides before the metal could reach the mold basins.
The molten alloy poured into the top pouring basins, disappearing down the upright gates into the dark sand below.
A deep, underground hiss echoed from the casting pit.
The two thousand-degree liquid metal struck the water-cooled iron core-pipes. Then, the straw rope burned into gas. The internal water boiled into a high-pitched scream of escaping steam.
Smoke curled from the sand vents as the organic fibers in the loam burned away.
For three minutes, the liquid metal rose steadily inside the molds.
Up through the barrel cavities it climbed. It filled the flared muzzle bells. It rose into the heavy feeder risers until white-hot metal pooled six inches above the top flasks.
“Pour complete,” Borin called, slamming a new clay plug into the fire taphole with a long iron rod.
The stream of liquid metal cut off.
Silence slammed down over the foundry. It was broken only by the hiss of cooling steam and the crackle of glowing melted rock waste in the sand.
Giles stepped up to the edge of the pit, inspecting the color of the cooling risers.
“Internal core cooling functioning within design settings,” Giles said, his voice calm and steady. “The inside bore is solidifying first. Meanwhile, the outer walls remain molten. As the outer metal cools and contracts, it squeezes inward against the solid core, pre-stressing the barrel into crushing hoop tension.”
Borin pulled off his leather gauntlets and wiped his bald, sweat-soaked scalp with a damp towel.
“Now comes the hardest part of casting,” Borin grunted, sitting down on an anvil horn.
“The cooling cycle,” Giles agreed. “Eighteen hours of slow, uniform cooling in dry sand. If anyone disturbs the molds before tomorrow noon, heat shock will crack the transoms.”
* * *
At noon the following day, the foundry pit was opened.
The sand was still warm to the touch, streaming a dry, earthy heat.
Duncan and four quarrymen hooked heavy hemp slings to the upper risers of the first mold, hoisting the four-hundred-pound casting out of the sand pit with the derrick crane.
Borin stepped forward with a heavy chipping hammer.
The dwarf hammered the baked loam casing. The brittle sand cracked, falling away in black, smoking chunks to reveal the gleaming metal beneath.
A collective murmur went up from the apprentices.
The newly cast barrel hung suspended in the sunlight.
It was an amazing, muscular metal tube of dark golden-bronze, veined with a subtle, grayish-iron sheen. Its surface was fully smooth, devoid of blowholes, cold-shuts, or shrinkage voids.
The heavy flared trumpet bell at the muzzle gleamed like polished amber.
Borin lifted his chipping hammer and struck the barrel’s breech a ringing blow with the flat of the head.
The metal didn’t thud. It sang.
A pure, ringing, sustained chime shook through the foundry, ringing clear as a silver bell for over twenty seconds.
Borin tossed his hammer into the sand, shaking his head in deep satisfaction.
“Listen to her sing,” Borin murmured, wiping his soot-stained brow. “Not a single blowhole. Not a seam. Ringing true from breech to bell. She’s solid as mountain granite.”
“A flawless casting,” Giles confirmed, measuring the pivot pin width with his fine measuring tongs. “Zero ovality. Shrinkage allowance was accurate to fifteen thousandths of an inch.”
Duncan and his men hoisted the second barrel from its sand bed. When Borin struck its breech, it answered with a matching clear pitch. A ringing pair cast to within a quarter-pound of each other.
Lady Millicent walked down from the casting deck, checking the weight scales.
“Eight hundred and forty pounds of finished ordnance,” Millicent noted, dipping her iron pen. “Total metal charge was nine hundred and sixty pounds. That represents an eleven point five percent melt loss, well under our fifteen percent scrap projection. The foundry has operated with exemplary thrift.”
The final operation was machining the bores.
Both heavy bronze-iron barrels were hauled on timber rollers to the grist mill machine shop. There, Caleb and Borin had built a water-powered level boring rig.
The first barrel was clamped rigidly to a heavy white oak sliding carriage.
Connected to the grist mill’s backup power shaft was a four-inch solid iron boring bar, fitted with hardened steel cutter bits forged by Borin from high-carbon mountain iron.
The mill water gate was opened.
The sixteen-foot waterwheel groaned, turning the boring bar at forty turns a minute through reduction gearing.
The steel cutter bits entered the rough casting, shaving away paper-thin ribbons of bronze-iron alloy with a high-pitched, steady hum.
A nonstop stream of cold spring water from the aqueduct water chute poured over the cutter head, washing away metal shavings and keeping the cutting edges cool.
For six hours, the waterwheel turned the boring bar on each barrel in set.
By sunset, the cutter emerged from the breech end of the second gun.
Giles brought up an approved four-inch brass tube-shaped plug gauge smeared with animal fat.
He slid the plug into the flared muzzle.
The four-inch metal tube glided down the four-foot bore with a smooth, airtight sharp air hiss.
“Four point zero inches bore width,” Giles announced, withdrawing the gauge. “Bore straightness true within two thousandths of an inch over forty-eight inches. Surface finish meets ordnance grade.”
Borin leaned over the muzzle. He held a small mirror into the throat to reflect lantern light down the mirror-smooth rifling-free metal tube.
“Look at that sheen,” Borin muttered, his thick thumb stroking the bronze-iron lip. “The copper-iron matrix is tight as drawn wire. When the blackpowder burns, the sulfur won’t find a single pore to bite into. We can fire twenty rounds without an acid wash.”
“Heat fading away is also improved by forty percent,” Giles noted, consulting his metalworking notes. “The copper conducts burning heat rapidly into the outer casing, preventing nearby throat softening during sustained fire.”
Caleb patted the oak carriage bed with pride. “We have the pivot mounts framed, Lord Giles. The bronze pivot pin caps are seated and greased.”
Kenneth Drake stepped up to the finished barrels. He ran his hand over the cold, gleaming bronze-iron bell, his scarred face solemn and watchful.
“Two of these in the outer gatehouse,” Kenneth said softly. “One aimed through the murder holes, one sweeping the bridge.”
“The recoil springs are tuned to absorb four inches of dynamic travel,” Giles added. “The four-inch anchor bolts are keyed directly into the concrete floor.”
Before Kenneth could reply, the door swung open.
Toby Karr hurried into the machine shop. His face was flushed and his arms piled high with bundles of copper wire, wooden sabot cups, and canvas sacks.
“Lord Giles, Master Borin,” Toby called. He set the supplies down on the workbench with a heavy clatter. “The sabot wadding is ready. Caleb finished turning twenty wooden cups on the pedal lathe. Mistress Teresa packed the felt disks with rendered animal fat. We have three thousand cast-iron pellets sorted in wooden tubs. We’re ready to assemble the ammunition. Master Borin has the powder scales waiting in the shop.”