[Someone]

You need lots of gunpowder inside the city in case you are attacked, so you need an armory inside the city.

Adding a factory doesn’t seem to add that much risk to me. It can be cordoned of in a building with strong walls and light-weight ceilings. That directs any force of an accidental explosion upwards.

The armory, on the other hand, needs protection against incoming projectiles. That calls for strong ceilings.

[gumby]

I don’t believe “gun”powder was used in weaponry in the Ming era.

Your logic is sensible but is not for this specific example.

[Someone]

I don’t know whether it did, but Wikipedia thinks it was used. https://en.wikipedia.org/wiki/Wanggongchang_Explosion:

“The epicenter was a major production center of gunpowder

[…]

a military storage facility that "dispatches 3000 catties (about 1.8 metric tons) of gunpowder every five days"”

This was 400 years ago, about 800 years after the invention of gunpowder (https://en.wikipedia.org/wiki/Gunpowder#China) and about 600 after the first primitive guns (https://en.wikipedia.org/wiki/Gun#History)

[gumby]

Learn something new every day. Thanks!