It was decided to carve large spiral grooves inside the musket barrels, but the craftsmen fell into another dilemma.
"Which direction should we make it spin?"
As they deliberated over the direction of the spiral grooves, Hyeong came to a conclusion.
"Wouldn't it be better to make one in the direction of the clock's hands when looking from the muzzle, and one in the opposite direction?"
At this, Choe Hae-san opened a slate and began calculations.
"Four types with rotations from half a turn to two turns, two types of rotation directions, and we need to check for deviations, so at least five each... that makes forty. It will take some time."
"We must put in the effort."
At Hyeong's words, the craftsmen present let out a small sigh. However, no one complained. The work was difficult, but as they fired the muskets, they found their spirits lifted, and there was a certain pleasure in verifying the results.
Of course, for Choe Hae-san and Lee Cheon, who were in the middle of it all, the headaches were more severe than the fun.
In the subsequent tests, all forty muskets performed beyond expectations. They could fire more than five shots without any issues, and there was little to no decrease in power.
However, during the analysis of the test results, an unexpected outcome emerged: the accuracy was higher than expected. Surprised by this unexpected result, Choe Hae-san submitted a report and made a suggestion.
"Until now, hitting five out of twenty shots at a distance of 70 paces was considered good luck. But in this test, all forty muskets hit the target at 70 paces. We need to conduct research on this!"
"Indeed. Let's do it! Prepare yourselves."
"Yes, Your Majesty!"
Seeing Choe Hae-san leave enthusiastically, Hyeong clenched his fist.
"Yes! We've got it!"
To find the cause of the unexpected results and ways to utilize them, Choe Hae-san, Lee Cheon, and the craftsmen fired hundreds of bullets. Through this process, the officials and craftsmen discovered several facts:
- The grooves inside the musket barrel performed best with one and a half turns.
- When the musket was securely fastened to the stand and fired, the bullet could hit a target up to 500 paces (about 600 meters) away. However, this meant hitting the target board, not the bullseye.
- The range did not increase due to the grooves; 2 taels (about 7.5 grams) of gunpowder could still fire a 5-tael (about 17 grams) bullet up to 800 paces (about 960 meters).
- At 500 paces, the bullet could not penetrate the iron plate used as a target, but it was inferred that it could cause significant injury to an enemy based on the dented state of the plate.
- The direction of the grooves should be unified with the direction in which the barrel and cap are tightened. If the opposite direction is used, the more shots fired, the more the barrel and cap would loosen.
"Your Majesty, should we experiment with increasing the amount of gunpowder?"
Despite Choe Hae-san and Lee Cheon's enthusiasm, Hyeong shook his head.
"There is a high possibility of repeating the problems of the existing musket barrels."
"Ahā¦."
"Instead, let's systematize the results we have secured."
"Yes, Your Majesty."
Hyeong, Choe Hae-san, and Lee Cheon classified the results as follows:
- Maximum Range: The farthest distance a bullet could travel when the specified amount of gunpowder and bullet were loaded and fired. The bullet's power is almost negligible.
- Maximum Effective Range: The distance at which at least 30% accuracy can be expected when aiming and firing. However, the bullet must maintain enough power to cause significant injury to the target.
- Effective Range: The maximum distance at which trained musket soldiers can hit a target when aiming and firing.
According to the classification by Hyeong, Choe Hae-san, and Lee Cheon, the performance of the musket barrels with spiral grooves was as follows: maximum range of 800 paces, maximum effective range of 350 paces, and effective range of 250 paces.
As Hyeong, Choe Hae-san, and Lee Cheon expressed considerable satisfaction with the results, the officials and craftsmen in the research institute were pondering over the homework Hyeong had given them.
"Analyze why the performance of the musket barrels suddenly improvedā¦."
"From the test results we've seen so far, the only reason for such a significant improvement in performance is the spiral grooves. But why did this happenā¦."
"That's the problemā¦."
The most likely suspect was the 'spiral grooves,' but the officials and craftsmen could not easily understand what these grooves did.
While the officials and craftsmen were in deep thought, a bowmaker from the Military Equipment Bureau offered an opinion.
"Isn't it because the grooves make the bullet spin?"
"Make the bullet spin? Can you explain more?"
The bowmaker gestured with his hands and explained in more detail.
"When you attach feathers to an arrow, you do it slightly off-center. This makes the arrow spin and fly straight. It also reduces the effect of crosswinds."
"Is that so?"
Finding this plausible, the officials and craftsmen conducted tests with bullets of various sizes. The results confirmed that bullets that engaged with the protruding parts of the spiral grooves and spun showed improved accuracy.
All the knowledge discovered and the data obtained during the testing process were documented and strictly stored in the deepest vault of the same level.
"This is a top-secret matter related to our nation's defense, so everyone must keep it confidential."
At Hyeong's warning, the officials and craftsmen responded in unison.
"We will remember this well!"
* * *
This confidentiality was maintained even during the inspection. Choe Hae-san did not reveal the part about the spiral grooves while explaining the process of making the musket barrels to Sejong.
Sejong only learned about this part after the inspection. In a private meeting with Sejong, Choe Hae-san submitted a written report, and after reading it, Sejong nodded.
"I understand why the Crown Prince and the others kept silent. Then, I must do the same. Sang-seon, bring the fire pot."
Sejong threw the report into the fire pot and burned it.
Meanwhile, as Choe Hae-san was reporting to Sejong, Hyeong muttered to himself while reviewing the related records.
"If the performance of the musket barrels becomes known, it will definitely leak. Whether it's captured during battle, stolen, or sold for a profit. And they will enthusiastically replicate it. But by the time they understand the principles and try to improve it, we will be one step ahead. That's why we're pushing this so hard."
* * *
"Let me say again, you have truly created an excellent weapon."
"The musket barrels to be used by the musket soldiers will be standardized to this new type."
As Hwang Hee was about to say something, Sejong raised his hand to stop him.
"Hmmā¦ If we start deploying them sequentially from the northern regions, it should be fine. Good! Let's review this plan."
"Your grace is boundless!"
"Your grace is boundless!"
As Sejong gave a positive decision on the production and deployment of the new musket barrels, Hyeong, Choe Hae-san, Lee Cheon, and other officials bowed and exclaimed, "Your grace is boundless!"
"Is that so? Have you decided on the musket barrels?"
"No, there is another type. The Mounted Musket Barrel (馬äøéē)."
"Really?"
Seeing Sejong's interest, Choe Hae-san gestured. A soldier in blue armor entered and opened a long leather pouch at his waist, taking out a silver musket barrel and holding it with his arm bent, pointing the muzzle upward.
"I want to see it in detail."
"Yes, Your Majesty."
At Sejong's command, the soldier held out the musket barrel on his palms respectfully. Sejong examined the musket barrel from all angles and stopped at the round iron tube in the middle.
"Six holes? Surely, this musket can fire six shots?"
"You are correct."
"Wow!"
Seeing Sejong's surprised expression, Hyeong smiled and replied.
"One of the masterpieces from Area 51."
'Of course, the design was already there, butā¦'
The musket in the soldier's hand was a modified version of the 'Colt 1860 Arm' to fit the Korean military situation. This was something Hyeong had prepared as a follow-up to the Kentucky Rifle during his time in the 21st century.
Sejong, after receiving the musket barrel from the soldier, said,
"I want to see how it fires."
"Yes."
In the demonstration, the soldier hit all six targets set up 30 paces (about 36 meters) away. The target boards, retrieved and brought by the craftsmen, had six neat holes. The craftsmen turned the boards around, revealing iron plates embedded in the red cloth behind them.
Sejong and the ministers carefully inspected the target boards. As he checked, Jo Mal-seng shared his thoughts with Sejong.
"At least the Jurchens and the Japanese pirates who come within 30 paces will see hell."
"Is that what you think?"
"Yes!"
Seeing Jo Mal-seng's firm statement, Sejong looked at Choe Hae-san and Lee Cheon. Their faces, seasoned in military affairs, were full of confidence. Sejong nodded after confirming their expressions.
"I can see from your expressions. Now, about the armorā¦"
"Please forgive me, Your Majesty. There is still another weapon to introduce."
"Still more?"
Sejong's face showed a slight weariness. The effort put in by the Crown Prince and his subordinates was evident just from the musket barrels he had seen.
If gunpowder and musket barrels could be properly supplied, securing the safety of this Joseon would be as easy as turning a palm.
'No, with a little more effort, we might even recover the old territories of the Three Han, as my brother Yangnyeong said!'
As he tried to suppress this budding ambition, Choe Hae-san was fanning the flames again.
Just as Sejong was about to leave, he sat back down at Choe Hae-san's words.
"General! Proceed!"
"Your grace is boundless. The weapon I will introduce this time is a fire bomb (ē«å½), so we need to move to a different location."
"Your Majesty, a man's legs are like the pillars of a house. The house is strong when the pillars are strongā¦"
As Hyeong was about to give a long speech on health, Sejong quickly interrupted.
"ā¦ Let's walk, walk."
"Strong legs can prevent uprisingsā¦"
"Walk, I said! You, son, are quite talkative! You always talk about uprisingsā¦ How did I end up with such a sonā¦."
Sejong, muttering to himself, took larger steps with more force.
* * *
The place Choe Hae-san and Lee Cheon led Sejong to was even larger than the previous demonstration area. Not only was it larger, but a higher and thicker earthen wall was also built.
In front of the platform where Sejong and the ministers were seated, a wall made of sandbags was even higher and thicker than before. On the opposite side, the foothills of Mugeum Mountain began, and a bare patch of land at least 50 paces wide was visible.
"Did you cut down the trees?"
"Yes, to prevent a fire."
"Indeedā¦."
As Sejong and the ministers took their seats on the platform, the waiting craftsmen and soldiers brought a large table and placed various devices on it.
Choe Hae-san, standing next to the table, began his introduction of the new weapon.
"The fire bomb I will show you now is launched from a bowl-shaped cannon (ē¢å£)."
Choe Hae-san pointed to the round iron fire bomb with a command stick.