When Hyang returned, Sejong declared the end of the demonstration.

"With this, I will conclude the demonstration. I will provide food and drink for the hardworking soldiers, so let them enjoy the feast."

"Wow!"

"Long live Your Majesty! Long live!"

Though the demonstration had ended, Hyang shook his head and left the gathering.

"I can't take it anymore. My curiosity is unbearable."

Leaving the venue, Hyang continued to investigate with the artillery and cannon soldiers.

"I apologize for holding you up when His Majesty has graciously prepared a feast."

"No, it's fine!"

"Not at all!"

The cannon and artillery soldiers waved their hands, denying Hyang's apology.

"I won't let you feel neglected, so please help me just a little."

"No, please just give us your orders!"

"Thank you. First... what difficulties do you have in using these cannons?"

At Hyang's question, the cannon soldiers paused for a moment before sharing their concerns.

- It's hard to use.

Except for the cannon that is mounted on a cart, the others require a bag to be inserted into the cannon, making it difficult for even a strong soldier to fire more than two shots.

- The effective range to completely suppress the enemy is too short.

When firing a small charge with the cannon, it can reach about 240 meters, but hitting the target accurately is difficult.

Considering the time it takes to reload, they use a method to shoot multiple arrows at once, but that requires drawing the enemy in to at least 50 meters.

To ensure a hit, they need to shoot within 40 or even 30 meters.

"Hmm... I see."

While recording the soldiers' words, Hyang looked at the cannon they were holding.

"Is this the cannon? May I hold it?"

"Yes."

As Hyang held the cannon, he muttered softly, "What on earth... is it a problem with the center of gravity? How much does this cannon weigh?"

At Hyang's question, Choi Hae-san answered immediately.

"It weighs about 2.2 kg and is approximately 44.6 cm long."

"And the length of the bag?"

"It isn't precisely determined, but it should be at least 1.2 meters."

"Yet the lengths seem to vary quite a bit?"

At Hyang's observation, Choi Hae-san replied with a troubled expression.

"It varies slightly depending on which measurement system is used."

"Really..."

Hyang clicked his tongue at Choi Hae-san's answer.

Now that he thought about it, the sizes of the cannons the soldiers were holding were all different.

This was a problem that spanned the Joseon era.

The standards for measuring length in Joseon were ambiguous, with various systems like Hwangjongcheok, Yeongjocheok, and Jollyeogicheok being used.

"Isn't it basic to unify the measurements when manufacturing?"

"Since we receive them as tribute..."

"Tsk!"

While looking at the cannon, Hyang tilted his head. 'Even if the center of gravity is tilted forward, considering the soldiers' sizes, it shouldn't be a situation where they can't fire more than two shots.'

No matter how he thought about it, Hyang couldn't understand, so he asked out of curiosity, "How much gunpowder do you put in the cannon?"

"One yang."

"Gasp!"

"Your Highness! What is the matter?"

Seeing Hyang's shocked expression, the nearby soldiers, commanders, and Choi Hae-san rushed over.

Hyang waved his hands in a hurry.

"It's nothing! Nothing at all! I was just surprised that there was more gunpowder than I expected!"

"Oh, I see..."

Upon hearing Hyang's response, the others finally relaxed. 'I found it! This is the culprit!'

Thinking he had identified the source of the problem, Hyang hurriedly organized his notes.

"I have learned everything I need. General, I will send meat and wine through my attendant, so please distribute it to them."

"Thank you very much!"

All the commanders and soldiers expressed their gratitude at Hyang's words.

Hyang lightly waved his hand.

"This is for those who work tirelessly for Joseon. Eat well and gather your strength to fortify the defense of our nation."

"We will remember and carry out your orders!"

On the way back to the palace after the demonstration, Hyang spoke with Choi Hae-san.

"Is the cannon operated in pairs like that?"

During the demonstration earlier, the cannon soldiers operated in pairs.

One soldier firmly held the cannon's bag while another lit the fuse.

Once the shot was fired, the waiting soldier handed over a pre-loaded cannon, and the soldier holding the bag prepared to fire again.

In response to Hyang's question, Choi Hae-san answered immediately.

"Basically, it is operated in pairs."

"What if one person operates it alone?"

"They would hold the bag with their right hand and light the fuse with their left, or they would tuck it under their right arm and hold it with their left while lighting it with their right."

"That doesn't sound comfortable."

At Hyang's observation, Choi Hae-san nodded.

"That's right. So, operating in pairs is the standard, but there is a problem with the demand for troops, making it difficult to expand the cannon units."

Choi Hae-san's disappointed expression reminded Hyang of a famous advertisement from the 21st century.

- It's great for men, but what can I say?

Nodding at Choi Hae-san's explanation, Hyang replied, "That makes sense. To properly fire the cannon alone, it seems one would need at least the strength of a two-headed four-kidney."

"Yes? Hahaha! That's right!"

Upon returning to the palace, Hyang opened a blank book and murmured, "The culprit was the amount of gunpowder."

In the 21st century, while in America to build a warship, Hyang had met many enthusiasts.

Among those he met, many were military fans, especially those who collected and fired classic steam weapons.

There was one person he had become friendly with, who had a collection of rifles from the American Revolutionary War to firearms from World War II, all at a museum level.

Not only did he collect firearms, but he also enjoyed shooting, even buying black powder in bulk to make his own cartridges.

Just before returning to Korea, when Hyang visited his house, he happened to witness him reloading ammunition for a Henry rifle.

"Isn't this the gun from the Western movies?"

At Hyang's question, the enthusiast smiled and replied, "That's a Winchester, and this is its predecessor."

"How much gunpowder do you put in?"

"30 grains."

As he continued explaining, the enthusiast reloaded the cartridges, noting that the amount of black powder for a .

44-40 cartridge was 30 grains.

"30 grains seems small, doesn't it?"

"No, no. 30 grains, not grams."

"Oh..."

For reference, the amount of black powder used at that time converted to about 2 grams.

With that 2 grams, he could launch a 14-gram lead bullet at supersonic speed.

"Though black powder is said to have about half the power of smokeless powder, with one yang, it should at least have the power of a . 50 caliber... If they hold it so awkwardly, it's bound to cause problems..."

Hyang recalled a video he had seen on the internet in the 21st century.

It was a demonstration scene from a weapons expo in the Middle East, showcasing a large-caliber hunting rifle experience.

The clumsily held rifle by the Arab men caused them to tumble around, while the last person who seemed properly trained shot perfectly without such antics.

Remembering that video, Hyang sighed.

"Without a proper aiming device, they have no choice but to shoot in the general direction, and to see any effect from that, they have to stuff arrows or projectiles in there, and for those projectiles to work properly, the amount of gunpowder has to increase, leading to soldiers getting hurt... It's a vicious cycle. Sigh..."

After sighing, Hyang concluded, "I need to create proper personal firearms first. But before that..."

The next day, Hyang sought out Choi Hae-san immediately.

"General, I have something to ask."

"I will answer sincerely."

"Are all the fuses used in the cannon of the same thickness?"

"Yes, they are."

"Is it possible to obtain those fuses now?"

"Please wait a moment."

Choi Hae-san asked for Hyang's understanding and called someone to give orders.

A short while later, the person returned with the fuses and handed them to Choi Hae-san.

"Your Highness, here they are."

"Could you light a candle for me?"

"Yes? Yes."

Receiving the fuses, Hyang brought them close to the lit candle.

Sizzle!

As the thick smoke rose and the fuse caught fire, Hyang blew on it.

Whoosh!

As Hyang blew, the burning fuse fizzled out.

He conducted the same experiment with the other fuses, and similar results followed.

Seeing the results, Hyang nodded.

"Indeed... General, do you understand what the problem is?"

Choi Hae-san nodded at Hyang's question.

"Yes. The fuses are weak against the wind."

"Weren't there any reports about this issue?"

"There weren't. If the fuse goes out in the wind, we can just replace it and light it again."

Choi Hae-san's response, which seemed to downplay the issue, made Hyang's expression sharpen.

"In a time-sensitive battlefield? Immediately contact the military supply office and find a suitable thickness for the fuses."

"Understood."

A report from the military supply office arrived through the Ministry of Military Affairs a fortnight later.

"Upon receiving the Crown Prince's orders and conducting an investigation, we found that the diameters of the fuses for various types of cannons and artillery were 7 ri (about 2.1 mm). However, the fire would suddenly go out during firing, so we experimented by increasing the diameter by 1 ri, and the fire did not go out. However, there was no adjustment for the distance of the arrows or the depth of the targets. Therefore, we request that from now on, the diameters of the fuses for the cannons and artillery be set to 8 ri."

After reviewing the report, Sejong ordered the Minister of Military Affairs.

"The contents of the report are extremely correct, so adjust the diameters of all cannons and artillery fuses to 8 ri."

"Understood!"

After giving orders to the Minister of Military Affairs, Sejong wore a satisfied expression.

"Indeed, he is the Crown Prince."

Unbeknownst to Hyang, changing the thickness of the fuses was something that had actually been done by King Munjong in history.

While Sejong was only aware of the fuse issue, Hyang was busy working behind the scenes.

"These days, the Crown Prince has not been seen."

At Jeongcho's words, Lee Cheon replied, "He has been in the annex for five days now, searching for something very important in the books."

"An experiment?"

"Yes. He has been gathering various types of acids and mercury through the Military Supply Office and the Office of Astronomy."

"I see."

At Lee Cheon's response, Jeongcho turned his gaze toward the annex built on one side of the East Palace.

Following Hyang's request, two annexes had been constructed right next to the East Palace.

The larger building was the main office where Jeongcho and others worked, while the smaller building was designated as Hyang's space for conducting experiments alone.

This small building had become a place that the researchers, along with Hyang's study, most wanted to enter.

"The Crown Prince has arrived!"

At the attendant's announcement, everyone who had been chatting straightened up.

A moment later, Hyang entered, holding a long wooden stick and a blueprint.

"Everyone, please take your seats."

"Yes."

Gathered around the large table in the center, they began their discussion under Hyang's lead.

"Have you all eaten?"

"Yes. And you, Your Highness?"

"I have eaten as well. I need to eat well at this age."

Breaking the ice with light banter, Hyang checked on the progress of their work.

"Minister Jeong, how is the revision of the calendar going?"

At Hyang's question, Jeongcho nodded lightly and replied, "There has been considerable progress. We have accurately identified the discrepancies between the Ming calendar and our seasonal calendar, and we are creating formulas to correct them."

"What about solar and lunar eclipses?"

"We are also working on calculations for that."

Jeongcho's answer brightened Hyang's face.

"Thank you for your hard work. So when can we expect the results?"

"I believe we can finish by the end of this year."

Hyang frowned at Jeongcho's response.

"The end of the year is too late. I would like to see the results by the Chuseok festival at the latest."

"Chuseok festival?"

At Hyang's command, Jeongcho's face turned pale.

They were already working late into the night with Jeong In-ji.

Having prepared for the worst, they had aimed to finish by the end of the year, but now the Crown Prince wanted it even sooner.

Seeing Jeongcho and Jeong In-ji's faces turn ashen, Hyang added, "If necessary, recruit additional officials skilled in arithmetic. If two are struggling, three can help, and if three are struggling, four or five can do it, right?"

"There aren't any who want to come..."

At Hyang's words, Jeongcho spoke with a troubled expression.

Among the officials working in the palace and the six ministries, rumors circulated that "if you go to the Hall of Worthies, the king will make you work hard, and if you go to the research institute, the Crown Prince will make you work hard."

"As I said before, bring them in under my name. Why are such high-ranking officials being so timid?"

At Hyang's reprimanding tone, Jeongcho bowed his head.

"I will follow your orders."