Inside the cannon, it was decided to carve a large spiral groove, but the artisans fell into another dilemma.
"In which direction should we twist it?" As they pondered the rotation direction of the groove, Hyang reached a conclusion.
"When viewed from the muzzle, we should make one twist in the clockwise direction and one in the opposite direction, right?" Hearing this, Choi Hae-san opened a board and began calculating.
"With rotations ranging from half a turn to two turns, that’s four types, and since there are two rotation directions, we need to check the variations, so at least five barrels… That makes it forty barrels. This will take some time."
"We must put in the effort."
At Hyang's words, the artisans let out small sighs.
However, no one complained.
The work was hard, but firing the cannon was surprisingly refreshing, and there was a certain enjoyment in checking the results.
Of course, for Choi Hae-san and Lee Cheon, who were caught in the middle, the fun was overshadowed by headaches.
In the subsequent tests, all forty barrels showed results beyond expectations.
Each barrel could fire more than five shots without any issues, and there was little sign of power loss.
However, during the analysis of the test results, an unexpected outcome emerged: the accuracy was higher than anticipated.
Excited by this unforeseen result, Choi Hae-san submitted a report and suggested, "Until now, at a distance of seventy paces, firing twenty shots would yield about five hits, which was considered lucky. But in this test, all forty barrels hit the target at seventy paces. We need to study this further!"
"Indeed. Let’s do it! Prepare!"
"Yes, my lord!"
Watching Choi Hae-san leave in high spirits, Hyang clenched his fist. 'Yes! We’ve got something!' To find the cause of this unexpected result and how to utilize it, Choi Hae-san, Lee Cheon, and the artisans fired hundreds of rounds.
Through this process, the military officers and artisans learned several facts:
- The number of rotations of the groove inside the cannon achieved optimal performance at one and a half turns.
- When secured tightly to the fixture and fired, the bullets could hit targets up to five hundred paces (about 600 meters) away.
However, this meant hitting the target board, not a direct center hit.
- This did not mean that the firing distance from the cannon had increased.
Regardless of the presence of grooves, 2 don (about 7.5g) of gunpowder could propel a 5 don (about 17g) bullet up to 800 paces (about 960m).
- At a distance of five hundred paces, the bullets did not penetrate the iron target used.
However, judging by the deformation of the iron target, it was estimated that it could inflict considerable injury on the enemy.
- The direction of the groove's rotation should be unified with the tightening direction of the cannon's body and cap.
If reversed, the more shots fired, the looser the cannon's body and cap would become.
"My lord, what if we increase the amount of gunpowder for the experiment?" Choi Hae-san and Lee Cheon showed enthusiasm, but Hyang shook his head.
"There is a high possibility of repeating the existing cannon's problems."
"Ah..."
"Instead, let’s systematize the results we have secured."
"Yes, my lord."
Based on the results they investigated, Hyang, Choi Hae-san, and Lee Cheon classified them as follows:
- Maximum Range: The farthest distance achieved when firing with the specified gunpowder and bullet.
The bullet's power is almost negligible.
- Maximum Effective Range: The distance where at least a 30% hit rate can be expected when aiming and firing.
However, it must maintain enough power to inflict a certain level of injury on the target.
- Effective Range: The maximum distance at which trained cannon soldiers can hit the target when aiming and firing.
According to the classification made by Hyang, Choi Hae-san, and Lee Cheon, the performance of the cannon with the spiral groove was a maximum range of 800 paces, a maximum effective range of 350 paces, and an effective range of 250 paces.
While Hyang, Choi Hae-san, and Lee Cheon expressed considerable satisfaction with their classification of the results, the officials and artisans of the research institute were pondering how to solve the task Hyang had presented: "Analyze why the performance of the cannon has suddenly improved."
"From the results of the tests we've conducted, the only reason for this dramatic performance increase is the rotation of the groove. But why did this result occur…?"
"Exactly. That’s the problem…" The most likely suspect was the 'rotating groove,' yet the officials and artisans could not easily understand what the groove had done.
While the officials and artisans were deep in thought, a craftsman from the military's equipment department spoke up.
"Could it be that the groove causes the bullet to spin?"
"Causes the bullet to spin? Please elaborate."
The craftsman gestured and explained in more detail.
"When fletchers attach feathers to arrows, they do it slightly askew. This way, the arrow spins as it leaves the bow. What happens then is that the arrow flies straight. It is less affected by crosswinds."
"Is that so?"
It sounded plausible.
The officials and artisans varied the size of the bullets and entered into testing.
As a result, it was confirmed that bullets spinning in alignment with the protruding parts of the rotating groove improved accuracy.
The knowledge discovered and the data obtained during the testing process were all documented and carefully stored in the deepest vault of the research institute.
"This is a top-secret matter connected to our nation's defense, so everyone must be mindful of confidentiality," Hyang warned, and the officials and artisans responded in unison.
"We will keep it in mind!"
This confidentiality was maintained even amidst the ongoing inspections.
Choi Hae-san explained the process leading to the creation of the cannon to Sejong, but he did not reveal anything about the rotating groove.
Sejong learned of this detail only after the inspection was over.
Alone with Sejong, Choi Hae-san submitted the written report, and after Sejong read through it, he nodded.
"I understand why the Crown Prince and the officials kept silent until the end. Then I too must follow suit. Sang-seon, bring the furnace."
Sejong threw the read report into the furnace and burned it.
Meanwhile, while Choi Hae-san was reporting to Sejong, Hyang muttered while reviewing the related records.
"If the performance of the cannon becomes known, it will surely leak. Whether it’s through capture during battle, theft, or selling it for backhanded deals. And they will eagerly replicate it. But when they try to understand the principles and make improvements, our nation will be one step ahead. That’s why we are rolling this out."
"Once again, we have created a truly excellent weapon."
"The cannons used by the cannon soldiers will be unified under this new type."
As Choi Hae-san spoke, Hwang Hee was about to say something, but Sejong raised his hand to silence him.
"Hmm… If we start deploying them sequentially from the northern regions, that would be good. Very well! Let’s review that plan."
"Your grace is boundless!"
With Sejong reaching a positive conclusion regarding the production and deployment of the new cannon, Hyang, Choi Hae-san, Lee Cheon, and the other officials all bowed in unison, exclaiming, "Your grace is boundless!"
"Is this the decision regarding the cannon?"
"No, there is another type of cannon. It is the Ma-sang cannon."
"Oh?"
As Sejong showed interest, Choi Hae-san gestured.
At his gesture, a military officer clad in blue armor entered.
"The color of the armor…"
"This is the new armor we developed together. I will explain further later."
"Is that so? Then proceed."
At Sejong's command, Choi Hae-san continued.
"What I will show you now is the Gapsik Ma-sang Small Cannon."
As Choi Hae-san finished speaking, the military officer opened the lid of a long leather pouch he was wearing at his waist and pulled out a silver cannon, raising it with the muzzle pointing upwards.
"I wish to see it closely."
"Yes, your grace."
At Sejong's command, the officer presented the cannon respectfully with both hands.
As Sejong examined the cannon, his gaze stopped at the round iron tube attached to the center of the cannon.
"Six holes? Could it be that this cannon can fire six shots?"
"That is correct."
"Ah!"
Sejong was greatly surprised and turned to Hyang.
Seeing Sejong's astonished expression, Hyang smiled and replied, "It is one of the masterpieces from District 51."
"Of course, the design was originally existing," but what the officer held was a modified version of the Colt 1860 Arm tailored to the situation of the Joseon army.
This was something Hyang had prepared as a follow-up to the Kentucky Rifle during his time in the 21st century.
Upon hearing Hyang's response, Sejong returned the cannon to the officer and said, "I wish to see how it fires."
"Yes."
In the subsequent demonstration, the officer hit all six shots at a target set up thirty paces (about 36m) away.
The target board brought back by the artisans had six clean holes drilled through it.
The artisans turned the target around.
Behind the red cloth with the bullseye, iron darts were neatly embedded.
Sejong and the officials carefully examined the target board.
As they checked the target, Jo Mal-saeng shared his impressions with Sejong.
"At least the Jurchens and Japanese pirates that come within thirty paces will see hell."
"Do you think so?"
"Yes!"
At Jo Mal-saeng's assertion, Sejong looked at Choi Hae-san and Lee Cheon.
The faces of these seasoned military men were filled with confidence.
Seeing their expressions, Sejong nodded.
"I can tell from your expressions. Then, regarding the armor—"
"I apologize, your grace. There is still a weapon I need to introduce."
"Still?"
Sejong's face slightly paled.
Just the cannons he had seen so far reflected the hard work put in by the Crown Prince and those beneath him.
If they could properly supply gunpowder and cannons, securing the safety of Joseon would be as easy as flipping a palm.
'No, with just a little more effort, we might restore the realities of the old Samhan, just as my brother Yangnyeong said!'
As this budding ambition stirred within him, Choi Hae-san was reigniting the flame.
Just as Sejong was about to leave, he sat back down at Choi Hae-san's words.
"General! Proceed!"
"I apologize, but the weapon I am introducing this time is a fireball, so we must move to a different location."
"… Lead the way."
"Yes, your grace."
Following Choi Hae-san's guidance, Sejong moved along.
"This distance is quite far?"
At Sejong's slightly breathless remark, Hyang explained the reason.
"Given the location…"
"Should we have ridden horses?"
"Your Majesty, a man's two legs are like the pillars of a house. If the pillars are strong, the house becomes strong…"
As Hyang began to give a long speech about health, Sejong hurriedly interrupted him.
"… I will walk, I will walk."
"If the legs are strong, it will also prevent illness…"
"I said I will walk! You, child, talk too much! Every time you mention illness… How did I end up with such a child…."
While he continued to grumble, Sejong put more effort into his steps and walked on.
Choi Hae-san and Lee Cheon guided Sejong to a location larger than the previous demonstration area.
Not only was it larger, but higher and thicker earthen walls had been erected.
In front of the platform where Sejong and the officials sat, a wall made of bags filled with earth was even taller and thicker than before.
On the opposite side, the foothills of Mount Myeok began, revealing at least a fifty-jo area of bare ground.
"Did they cut down the trees?"
"Yes, to prevent fires."
"How thoughtful…"
As Sejong and the officials took their seats on the platform, the waiting artisans and soldiers brought a large table and soon placed various items on it.
Standing beside the table, Choi Hae-san began to introduce the new weapon.
"The fireball we are about to show you is launched using a bowl."
Choi Hae-san pointed to a round fireball made of iron with his baton.
"We have named this fireball 'Flying Thunderbolt'."
"Flying Thunderbolt… Is it a type of Jincheonlo?"
"What is Jincheonlo?"
"I have only seen it in records, but it is said to be similar to Jilryeopotong. It is recorded that Song and Jin used it."
"Is it called 'Flying' because it uses a bowl?"
As Choi Hae-san explained, the officials reminisced and shared their thoughts.
Observing the reactions of the officials, Hyang smirked.
"When we think of Munjong, we think of the Shin Gi Jeon and the Hwacha, but we must not miss the clichés! The clichés among clichés! In the sea, there is the turtle ship, and on land, there is the Flying Thunderbolt!"