In Bullet Angel there are 2 types of Gun, Gun that has expired date and Gun that you can get permanently (Forever).
Here I will teach you on how you can unlock Permanent guns without top-up any money.
Most of the permanent guns that you need to unlock are inside Event tab. So first thing is to go into Event tab.
♦Now you will see Daily Event, Recommended Activities, and Notice.
Start with Daily event you will see tasks that you need to complete to get For example:Ladder coin. When you complete all the tasks you can use that ladder coin to exchange a permanent gun in the store.
To exchange a permanent gun with your Ladder coin you need to go into Store > Exchange > Ladder coin and you will see all the items there.
Move onto Recommended Activities, Currently there are 2 events inside Recommended activities tab, however there will be more once the update come.
Let take Ghost Trace event as an example to explain: Inside the event tab you will see the task provided, complete those tasks and you will receive the Ghost Trace coin.
The ghost trace coin can be exchange in the tab below name "GHOST GIFT", once you get enough ghost coin you will be able to exchange for a permanent gun.
Note: This applied to all other events that are inside Recommended Activities.
Note: Always keep your eyes on the Event tab and the tab below it, to see if there is any other new event or exchange shop.
In conclusion, Bullet Angel permanent guns is not hard unlock, you just need to browse around the event tab more often and complete all the tasks to get the coin so you can exchange for the gun without spending real money into the game.