Magic and technology are opposites. Magic bends physical law to the will of the mage. Technology depends on physical law. In the arena the use of technology reinforces physical law, countering the effect of magic.
A magic using individual casting an offensive spell works by summoning some form of fire/ lightning bolt / ice/ acid etc. out of thin air (physically impossible!), and then accelerating that flame/ lightning bolt/ ice shard/ acid spray to high speed along a finely controlled trajectory, merely by force of will (also physically impossible). In contrast, a gun takes advantage of several physical laws to achieve the same ends.
If we accept the possibility of magic in textual combat then the reality of firearms does not become anything other than another form of attacking your opponent. Bullets do not automatically kill your opponent; they do not automatically penetrate armor any more than a spell does. Like all T1 attacks prepping is required to do substantial damage. With firearms it is more difficult to attain the ‘preps” because you cannot continually aim at the target.
Prepping is achieved easily with ‘powered’ weapons such as lasers and particle-beam guns by simply stating that the character is powering the weapon up. With gunpowder weapons it is more difficult. I have in the past used the word focused, focusing, focus on etc. to build up ‘preps’. This allows for cues that the opponent may see as the gunfighter is targeting them. These cues are no different than prepping a spell with the descriptors congruent with the magic the caster is employing.
Other than that gunfighters and spell casters are very similar, both require preps to establish the power to break through their opponents prepped defenses. As for bullets, guns fire a maximum of three bullets per attack and guns do run out of ammo, after ‘X’ number of attacks.
How does Focus work as a prep, and what of magical guns?
Focused is akin to being more accurate when fired. Other than that a firearm follows all conventions of a T1 attack be it magical, melee, brawling, psionic etc.
Magic based guns are like energy weapons you simply imply the weapon is charging.