"Making the original version of the Bi-gyeok-jin-cheon-loi is too inefficient."
The original Bi-gyeok-jin-cheon-loi used a solid cast sphere.
By the standards of the 21st century, this method had many issues.
Of course, creating a hollow spherical shell was technically impressive, but it was not a method I would recommend in terms of production efficiency.
"Looking at the performance, it's obvious that 'shut up and mass-produce' would be better, so we need to use our wits."
The first step that Hyang took was to split the sphere of the Bi-gyeok-jin-cheon-loi into two halves.
Hyang modified the design so that one half of the hemisphere had female threads, while the opposite side had male threads.
When the two hemispheres were aligned and twisted together, they would form a complete sphere.
Hyang also applied threads to the part where the fuse would be inserted and the hole for the gunpowder.
By adding threads to the cover that secured the fuse and the cover that sealed the gunpowder, everything would be held more firmly.
With the prototypes created in this way, Hyang began the firepower tests.
"First, let's skip the process of launching from the toy."
"Yes, my lord."
As a result of the tests, the improved Bi-gyeok-jin-cheon-loi exploded magnificently, just as Hyang had expected.
"Amazing!" "How about sending it to the North immediately?" Lee Cheon and Choi Hae-san, who saw the test site turned into chaos, could not stop their admiration.
However, Hyang shook his head with a smile.
"There are still many things to test. We need to try the launch test first."
"Launch... I see. I forgot about 'Bi-gyeok.'"
In the subsequent launch test, the Bi-gyeok-jin-cheon-loi was successfully launched.
After confirming the results, Hyang moved on to the next task.
"Now, I will report to His Highness and arrange the deployment..."
"Alright! Then let's reduce the thickness of the shell. Let's start by reducing it by 1.5mm."
Following Hyang's command, the artisans created prototypes by reducing the thickness of the shell from 1.5mm down to about 1.2cm in increments of 0.5mm.
It was a process of trial and error, literally embedding it into the body.
"As you mentioned, when we launched with double the gunpowder in the toy, the thinnest thickness that withstood from launch to impact was reduced to 3mm."
"Then shall we try packing the gunpowder and experiment?" "Yes, my lord."
In the subsequent test, the Bi-gyeok-jin-cheon-loi, with a thickness reduced to 3mm, withstood the impact from launch and exploded properly.
Seeing the results, Choi Hae-san and Lee Cheon became greedy again.
"Since the results are good, let's report..."
"The explosion radius is too wide. There is a risk of our side getting hurt. Let's study ways to reduce the explosion radius while increasing lethality."
"Your command is correct. I will think it over."
Hearing Hyang's command, Choi Hae-san, Lee Cheon, the military officers, and the artisans began searching for the optimal solution.
However, it was difficult to find a way to satisfy the contradictory conditions of 'enhancing lethality' and 'reducing the danger radius' at the same time.
In the end, Hyang had to step in again.
"Bring me clay, paper, and iron rings the size of a fist." "…Yes, my lord."
When the artisans brought the materials, Hyang commanded them.
"Apply a thick layer of clay about half an inch thick on the inside of the Bi-gyeok-jin-cheon-loi's shell, and insert the iron rings densely. Then, once the clay dries, cover it with paper to secure it tightly."
The military officers and artisans, hearing Hyang's command, gasped in admiration.
"Ah! What a clever idea!" In the subsequent test, the improved Bi-gyeok-jin-cheon-loi reduced the danger radius compared to the first version, but its lethality was further enhanced.
As Hyang examined the results, he turned to Choi Hae-san and Lee Cheon.
"Let's improve it a little more. Just a bit more..."
"Yes, my lord."
In the next round of improvements, Hyang and the artisans engraved a checkerboard pattern of gold on the inside of the Bi-gyeok-jin-cheon-loi's shell.
They added another layer of iron rings.
After completing the second round of improvements, Hyang, upon seeing the results of the subsequent test, commanded Choi Hae-san and Lee Cheon.
"I think this is sufficient. If we go any further, future generations will think of us as bloodthirsty savages."
"Indeed!" At Hyang's words, Choi Hae-san and Lee Cheon nodded vigorously.
The scene created by the improved Bi-gyeok-jin-cheon-loi was a spectacle in itself.
"Now, let's report..."
"Now we need to improve the cannon that will fire this explosive."
"Huh?" At Hyang's words, Choi Hae-san and Lee Cheon looked dismayed.
Hyang observed the large cannon that would fire the Bi-gyeok-jin-cheon-loi.
"The amount of gunpowder that goes into the chamber is 35 nyang (about 1.3 kg)... The problem is that it is not an efficient shape."
What Hyang pointed out was the overall design of the cannon.
"Let's change the structure!" Hyang designed the cannon that would fire the Bi-gyeok-jin-cheon-loi in a traditional straight shape.
He created a barrel shape similar to the Western cannons of the 18th and 19th centuries.
"Is it too Western? I don't think so."
Looking at his drawing, Hyang tilted his head.
To be precise, the design Hyang created was closer to the medium cannon made by Joseon during the Daewon-gun era.
Hanging the blueprint with the cannon and barrel he envisioned, Hyang discussed with Choi Hae-san, Lee Cheon, and the artisans.
"Let's mount it on a large wheeled cart. This will improve mobility."
"If the mobility of the cannon improves when facing the Jurchens in the North, it will be much easier, won't it?" At Hyang's words, Choi Hae-san and Lee Cheon nodded.
Having sufficient combat experience from both the South and North, the two understood the advantages Hyang mentioned right away.
Lee Cheon, while examining the blueprint, concluded, "We will create a cart with the cannon mounted on it and another cart for the Bi-gyeok-jin-cheon-loi and gunpowder... If even two Bi-gyeok-jin-cheon-lois accompany us, the Jurchens will not dare to act recklessly."
With Choi Hae-san and Lee Cheon, who could be called the best experts on cannons in the Joseon army, agreeing on the cannon, the development of the cannon and barrel progressed rapidly.
The new cannon differed from the existing ones in that both the exterior and the back part of the internal chamber were rounded.
"General Choi, do you remember when we first tested the explosive?" "Yes."
"At that time, the soot made on the copper plate spread radially. I think this indicates how the energy from the gunpowder spreads when it explodes."
Hyang's words made Choi Hae-san nod thoughtfully.
"That seems likely."
"Then, if we round the back part of the chamber like this, won't the cannon become sturdier? It will have the same thickness from any angle."
Choi Hae-san, examining the blueprint closely, nodded.
"It seems worth trying."
After the first cannon was made, Hyang and Choi Hae-san immediately began testing it.
They filled the new cannon and the existing large cannon's chamber with double the standard amount of gunpowder and tightly sealed it with heavy stones.
In about four consecutive launches, the new cannon did not cause any issues, but the large cannon developed cracks at the lower corner of the chamber.
After confirming the results, Choi Hae-san opened the writing board and wrote, "The test results confirmed that making the back of the cannon and chamber rounded strengthens my design. It seems appropriate to improve other cannons or design a new cannon with a similar shape."
"... Thus, this Bi-gyeok-jin-cheon-loi, as well as the design of the cannon, has all gone through the hands of His Highness the Crown Prince."
Upon Choi Hae-san's explanation, King Sejong and the ministers looked at Hyang once more.
"You... now you tire me even to say how amazing you are."
At King Sejong's words, all the ministers nodded.
They were exhausted from witnessing the continuous stream of astonishing inventions.
No, the prime ministers and the Ho Jopansuh were calculating the budget needed for mass production in advance, feeling overwhelmed.
"I want to see that newly created cannon."
"As you command."
A moment later, two carts entered the demonstration area, each pulled by two horses.
"The first cart carries the cannon mounted on the barrel, and the second cart is loaded with the Bi-gyeok-jin-cheon-loi and gunpowder for the cannon."
"Hmm..."
Listening to Choi Hae-san's explanation, King Sejong examined the carts.
On the cart connected to the barrel, there were two wooden boxes.
"Those boxes contain the explosive and gunpowder that will be used immediately after firing the cannon."
The soldiers opened the lids of the boxes loaded on the cart.
As King Sejong inspected the boxes, he noticed small pouches inside.
"What are these pouches?" In response to King Sejong's question, Choi Hae-san opened a pouch and took out its contents.
"These are the fuses that determine the time until the explosion, the wick to light the fuse, and 1 nyang of quick-burning gunpowder to ignite the slow-burning gunpowder, all contained in a paper tube to be embedded in the Bi-gyeok-jin-cheon-loi."
Nodding at Choi Hae-san's explanation, King Sejong said, "I see. Since the slow-burning gunpowder does not ignite with a wick, it is lit with the quick-burning gunpowder. And the paper tube?" "Initially, we used bamboo, but due to uniformity issues, we made the tube from paper."
"I see. That's a good idea."
"It was the Crown Prince's insight."
When Choi Hae-san credited Hyang, King Sejong turned to Hyang.
"I can see your efforts."
Hyang attributed the credit to the soldiers and artisans.
While examining the cannon, King Sejong's gaze stopped at the back part of the cannon.
What caught his attention was the part connected to the cannon's base.
There stood a column engraved with threads, and beside the interlinked gears was a handle similar to a reel.
Next to it was a semicircular dial inscribed with the characters 'Won (違), Geun (近), and Cho-geun (超近).' "Crown Prince, what is this used for?" "Yes, it is to adjust the angle of the cannon to control the range."
"Adjust the range?" "Yes. Like this."
As Hyang spun the handle resembling a reel, the cannon's muzzle moved up and down.
Seeing this, King Sejong turned his head.
"So, you adjust the angle of the cannon to control the distance?" At King Sejong's question, Choi Hae-san immediately answered, "That is correct, Your Majesty."
"How?" "It works on the same principle as shooting a bow. When you aim at a distant target with a bow, you raise the bow to shoot at an arc, right?" "Ah!"
King Sejong nodded in admiration at Choi Hae-san's explanation.
Choi Hae-san pointed to the semicircular range finder and explained, "By aligning the angle of the cannon with this scale, we can adjust the distance from 300 to 500 paces."
As King Sejong examined the scale closely, he turned to Choi Hae-san and Lee Cheon.
"You must have put in a lot of effort to figure out this scale."
"Indeed."
Choi Hae-san and Lee Cheon nodded at King Sejong's words.
By chance, they discovered—though it was a coincidence mixed with Hyang's intention—this fact, and to measure it accurately, Choi Hae-san, Lee Cheon, and the artisans fired hundreds of Bi-gyeok-jin-cheon-lois.
To reduce unnecessary gunpowder consumption, Bi-gyeok-jin-cheon-lois filled with soil and gravel flew through the air without rest, and eventually, nearly a hundred new Bi-gyeok-jin-cheon-lois had to be made due to metal fatigue.
That was not all.
Many of the cattle raised in the farms near Area 51 could not withstand the stress caused by the loud explosions and died, resulting in a significant loss of wealth.
The meat from the cattle that died was served at the tables of the artisans and soldiers.
"If we can adjust the distance like this, it will yield better results in battle. Can this be applied to other cannons as well?" In response to King Sejong's question, Hyang answered, "The officials in the research institute are currently studying it."
"But?" Upon hearing the answer, King Sejong searched for a response among his ministers.
"Deputy Director Jeong, I trust you."
At King Sejong's words, Jeong Cho bowed his head and replied, "I will obey your command."
Jeong Cho's voice was filled with emotion. 'I still can't go home...'
Thanks to Hyang's previous command, the officials in the research institute were grasping the books recording the results of the cannon fire and were engaged in a 'war with numbers.' Hyang's command was to investigate the changing ranges under various and bizarre circumstances, create tables, and formulate them into formulas to create distance adjustment devices for each cannon.
Because of this, the officials in the research institute could only return home on the designated holidays—working nine days and resting one day.
Hyang strictly adhered to this rule.
However, there were periods when the officials voluntarily worked overtime.
That period was when they were fermenting the soybean paste.
Joseon was known as the 'land of sauces,' consuming a lot of soybean paste and soy sauce.
With high consumption, every household had jars of sauces, and the smell of soybean paste filled the residential areas of Hanyang.
Thus, the smell of sauces was familiar to the Joseon people.
However, even the Joseon people found the smell produced during the fermentation of soybean paste unbearable.
Especially in households with many members, they had to ferment a large amount of soybean paste, so the smell was more intense in the homes of high-ranking officials who had many servants and guests.
The palace also fermented a large amount of soybean paste, but due to its vast space, the smell was not that strong.
For this reason, officials tended to delay leaving the office as much as possible during the fermentation period.
In any case, due to the commands of King Sejong and Hyang, Joseon became the first nation in the world to create and apply a shooting table for cannons.
After examining the cannon and the accompanying equipment that fired the Bi-gyeok-jin-cheon-loi, King Sejong straightened his back.
"Hmm, it seems I've seen everything I need to see, but before checking the accounts, there is one last thing to confirm. The armor worn by the military officers and soldiers here is different from what I've seen before, so explain this."
"I have prepared it. I will guide you."