Hello! I suggest a very low damage, normal damage, fire-inflicting line for the Antigua, useful mainly for Lockdown.
To give the impression that it's for Lockdown, I'd imagine that the recipes for it would/could be sold by Sullivan.

The gun's main point won't be doing damage, it'll be to start fires. It'd be effective to keep recons visible, and would do PLENTY of fire damage to anyone with a glass cannon loadout.

Because of the low damage and lack of specialized damage, I doubt anyone will use this in the clockworks/missions. Oh well.

Since it's be so easy to hit things with Antiguas, I think the fire Antigua will only inflict weak fire, instead of the moderate fire that
Pepperboxes and Magma Drivers do. Not an expert on this part, that might be too easy to defend against.

Visually, it'll be a dull orange with some red after one upgrade, and bright yellow with some orange after the second upgrade. Maybe some smoke or fire effects. Oh, and it should ignore those big vertical wings, the way the Pepperbox ignores that giant barrel of darts.

Since it loses the wings, the charge should probably lose the bird. It could use a fireball that functioned similarly instead.

I do not have anything to suggest about the name, feel free to name it if you really want to.

Argent Peacemaker's Damage Table (against fiends and slimes)

-----------------------Stratum 1----Stratum 2--Stratum 3---Stratum 4-----Stratum 5---Stratum 6
Basic Attack-------10-11---------14-15-------26-28--------29-31-----------46-57--------62-67
Charge Attack-----23-24--------30------------63-67--------67---------------119-155-----172-191

5* Fire Antigua's Damage Table

-----------------------Stratum 1---Stratum 2--Stratum 3----Stratum 4-----Stratum 5---Stratum 6
Basic Attack-------5-6------------7-8-----------13-14--------15-16-----------23-28--------31-33
Charge Attack-----11-12--------15------------31-34---------34---------------59-78--------86-96

TL;DR: See title.