A siege was won not by the size of a wall, but by the moving thickness delivered per square yard of entryway.
In the dim light of Master Borin Bronze-Lung’s foundry, Giles Croft stood over an oak drafting table, his sleeves rolled above his elbows.
On the table lay the scarred bronze barrel of the original prototype under-road drain cleaner. It was the improvised weapon that had shattered Sir Gareth’s pavilion shield at the south ditch three weeks earlier.
Giles ran a steel feeler gauge down the inside of the flared bore.
Beside him, Borin held an oil lamp, squinting through his thick wire-mesh foundry goggles.
“Look at that throat,” Giles said, pointing to the burning chamber. “Severe erosion along the lower third of the chamber wall. Potassium sulfide residues from the pyritic propellant have chemically pitted the bronze surface to a depth of three-thirty-seconds of an inch.”
Borin scraped the pitted metal with an iron scratch-awl, grunting in displeasure.
“The bronze was too soft,” Borin admitted, shaking his copper-braided beard. “We melted down old church bells and carriage fittings. Church bell bronze is high in tin—eighty percent copper, twenty percent tin. Good for making a loud chime, but brittle under fifteen thousand pounds of explosive gas.”
“And the breech transom deflected four thousandths of an inch,” Giles added. He measured the pivot pin shoulders. “If we fire another full-charge grape-shot round through this tube, hoop stress will cause total fatigue failure at the pivot pin roots. The barrel will split like an overripe melon.”
Borin nodded grimly. “Aye. It would take a gunner’s head off and leave the gate wide open.”
Giles brushed away the bronze shavings and rolled out a clean sheet of heavy drafting thick parchment.
“Which is why we’re retiring the prototype,” Giles said. “We’re going to cast two purpose-built heavy ordnance pieces for the outer gatehouse murder holes. The Blunderbore Canister Batterer, Mark Two.”
Captain Kenneth Drake stepped into the foundry, his ten-foot iron-shod pacing rod held vertically like a sentry’s spear.
He looked down at Giles’s new blueprint, his veteran eyes tracing the thick, muscular lines of the proposed cannon.
“You called the first one an under-road drain cleaner, my lord,” Kenneth said with a dry, knowing smirk. “What’s this one? A chimney brush?”
“It’s a close-quarters canister projector,” Giles replied without looking up. “A high-speed moving area-of-effect crushing weight system. There’s no need for civilian euphemisms when designing citadel ordnance.”
He tapped the flared muzzle on the drawing.
“The barrel is four feet six inches long,” Giles explained, pointing with his brass rule. “The bore measures four inches at the breech, tapering out to a seven-inch flared trumpet bell at the muzzle. The bell doesn’t increase projectile speed. It induces controlled lateral gas spreading, creating an immediate thirty-degree cone-shaped scattering of the shot.”
Kenneth studied the drawing. “Thirty degrees. At fifty yards, how wide is the spread?”
“A twenty-four-foot kill-cone,” Giles said. “Covering the entire width of the outer raised stone road. Inside the outer gatehouse entry hall, the rebound of the shot against the granite walls creates one hundred percent target saturation. An armored shock squad in tight shield formation can’t evade three hundred and twenty faster-than-sound iron projectiles.”
Master Caleb Thorne-Wood walked over from the joinery bench. He held a curved wooden block carved from seasoned white oak.
“The sabot cup,” Caleb said, setting the block on the thick parchment. “Turned on the lathe, just like you sketched. Hollow bottom to cup the blackpowder gas, flat top to carry the iron pellets.”
Giles picked up the wooden cup, checking its rim with his fine measuring tongs.
“Three point nine eight inches outer width,” Giles noted. “A two-hundredths-of-an-inch clearance inside the four-inch bore. When the propellant ignites, the wooden cup expands slightly under gas pressure, forming an obturating seal. It prevents hot gases from blowing past the shot, eliminating bore scouring and boosting muzzle speed by fifteen percent.”
Borin leaned over the drawing, his thick, scarred fingers tracing the thick metal around the powder chamber.
“Look at the thickness of that breech,” Borin chuckled. His dwarven eyes shone with skilled delight. “Four inches of solid metal behind the touchhole. Heavy with heavy cast-iron pivot pin bands. A cannon that shoots a bucket of iron marbles. By the Forge, boy, this is the filthiest, most beautiful weapon I have ever seen.”
“It’s not beautiful, Borin. It’s functionally optimized,” Giles said. “Now we must address the metalworking.”
Giles dipped his iron pen into the inkpot and wrote out the alloy specifications.
“We can’t use bell bronze,” Giles said.
He dipped his pen again. “And pure mountain iron is too difficult to cast into dense, flaw-free tubes without a steam hammer. We’ll cast a bronze-iron composite alloy: eighty-eight parts copper, ten parts tin, and two parts refined mountain iron, deoxidized with glowing-sand.”
Borin blinked, pushing his wire-mesh goggles up onto his bald forehead. “Iron in bronze? Iron doesn’t like melting with copper, Lord Giles. The iron forms hard little lumps that ruin the casting.”
“Not if you introduce the iron as a copper-iron master alloy at twenty-two hundred degrees Fahrenheit,” Giles explained.
He showed Borin a metalworking phase diagram on the slate. “The iron dissolves uniformly into the molten copper matrix. That increases the pulling yield strength from twenty-four thousand to forty-two thousand pounds of pressure. It gives the alloy the toughness of bronze and the hardness of forged iron.”
Borin stared at Giles for three seconds, his jaw slack. Then he let out a low whistle.
“Dwarven smiths in the Deep Peaks keep that recipe locked in iron vaults,” Borin muttered. “How does a surface exile know how to marry iron to bronze?”
“It’s standard metalworking phase chemistry, Borin,” Giles said, closing his inkpot. “It’s published in town foundry manuals.”
Toby Karr hurried in from the storehouse. He carried a heavy clay pot jar packed with black granular powder.
“The corned powder from the drying shed, Lord Giles!” Toby said, setting it down carefully on a felt pad. “Master Borin screened it through horsehair sieves. The grains are all uniform as poppy seeds.”
Giles inspected the grains through his magnifying glass.
“Good corning,” Giles approved. “Uniform grain size ensures a constant burn rate. Uncorned meal powder burns erratically, creating pressure spikes that rupture gun breeches. Corned pyritic powder produces smooth, progressive deflagration.”
Sister Teresa appeared in the foundry doorway, holding a wooden tub of boiled sheep fat.
“The fat from the slaughterhouse is rendered and strained,” Teresa announced. She wiped her hands on her linen apron. “If this grease is to seal the weapons of defense, let it be blessed with clean water. We protect three hundred souls who have done no harm.”
Kenneth Drake stepped to her side, his voice unusually soft. “We protect them with iron, Sister. But the grease helps.”
“The grease preserves the rubber rings and prevents rust,” Giles noted. “Every clockwork component has its function.”
By afternoon, the foundry yard was filled with the preparations for the great pour.
Toby Karr and four apprentices were mixing the molding loam inside two large wooden troughs.
The molding mixture was not common dirt. It was three parts sharp river quartz dust sand, two parts heat-proof clay from the high shale bluffs, and one part dried horse manure mixed with chopped horsehair.
“Why the horse manure, Master Borin?” Toby asked, wrinkling his nose as he shoveled the pungent gray loam into a wooden flask.
“Combustible organic fiber,” Borin barked, tamping the loam around a turned wooden barrel pattern. “When the white-hot metal hits the sand, the manure burns away into carbon gas, leaving millions of tiny pores. The steam and gas escape through the sand instead of bubbling into the molten metal. If the gas can’t get out, your cannon blows up in your face.”
Toby nodded solemnly, shoveling with renewed care.
In the center of the foundry floor, two deep casting pits had been excavated into the dry bedrock.
The wooden patterns were withdrawn, leaving two flawless, bell-mouthed cavities in the baked sand molds. Into the center of each mold, Borin lowered a hollow iron core-pipe wrapped in straw rope, through which cold river water could be circulated during cooling.
“Internal core cooling,” Giles instructed, inspecting the core posture with his sighting scope. “Cooling the bore from the inside out creates crushing hoop stresses in the inner metal tube walls. That pre-stresses the metal. That let it withstand thirty percent higher internal pressure without bursting.”
Caleb Thorne-Wood stepped up beside the pit, holding a wooden framing template.
“I have framed the carriage beds from seasoned white oak,” Caleb reported. “Twelve-inch timbers, joined with keyed mortises and bound in quarter-inch iron straps. The pivot pin beds are lined with greased glowing-bronze bearings. The guns will depress to forty-five degrees downward, aiming straight through the outer gatehouse ceiling slots, or elevate to fifteen degrees upward to sweep the bridge approach.”
Kenneth Drake tested the depression arc on the wooden model, his hand steady on the iron lever.
“At forty-five degrees downward,” Kenneth muttered, “the blast will hit the stone floor of the entry hall and ricochet into every corner. There’s no dead ground. Anyone standing inside that vault will be caught in an inescapable iron hailstorm.”
“Rebound fragmentation physics,” Giles agreed. “The granite paving acts as an energy reflector. Even if an armored shock trooper crouches beneath a tall body-shield, the ricocheting shot enters beneath the rim.”
Lady Millicent Croft walked into the foundry. She carried her ledger and a pair of brass measuring tongs.
“The pig-iron shipment from Raymond Barlow contains twenty tons of high-grade ore,” Millicent said, checking off her delivery list. “Sulfur purity is ninety-eight percent. We have enough raw stock to cast both barrels and produce forty complete canister charges.”
“Forty rounds represents twelve thousand eight hundred iron pellets,” Giles noted. “Adequate for three sustained defensive engagements.”
Borin wiped sweat from his face. He looked across at the twenty tons of mountain pig-iron and refined sulfur barrels delivered that morning by Raymond Barlow’s freight wagons.
“We have the copper from the old still-heads,” Borin said. “We have the trade ring’s mountain iron. And the blast-fire coals are glowing white.”
The dwarf picked up a glowing pine torch, his copper beard catching the firelight.
“Stoke the tuyeres, lads!” Borin bellowed to his apprentices. “Open the draft bellows! We’re casting the Dragon’s Mouth tonight!”
The blast fire roared to life, sending a gout of white sparks roaring into the twilight sky above Grey Crag.