Is this "Gun Mage" Fighter subclass balanced?

Question

I've created this Gun Mage homebrew Fighter subclass. The intent is to make a fighter that can cast spells by engraving them into bullets that they fire. This is inspired by Gun Mages from Iron Kingdoms as released in the D20 creative commons 3.5 rules. And intended for the Spell Jammer setting for D&D 5e

I intend for the spell progression to follow that of a 1/2 caster. For the full subclass you can check my Gun Mage: Google Doc

Gun Mage

Gun Mage Table

Level	Prof. Bonus	Features	1st	2nd	3rd	4th	5th
3rd	+2	Arcane Bullet	3	—	—	—	—
4th	+2		3	—	—	—	—
5th	+3		4	2	—	—	—
6th	+3		4	2	—	—	—
7th	+3	Ricochet, Adaptable Shot	5	3	—	—	—
8th	+3		5	3	—	—	—
9th	+4		6	3	2	—	—
10th	+4	Elemental Shot	6	3	2	—	—
11th	+4		7	3	3	—	—
12th	+4		7	3	3	—	—
13th	+5		8	3	3	1	—
14th	+5		8	3	3	1	—
15th	+5	Snap Shot	9	3	3	2	—
16th	+5		9	3	3	2	—
17th	+6		10	3	3	3	1
18th	+6	Caster Shell	10	3	3	3	1
19th	+6		11	3	3	3	2
20th	+6		11	3	3	3	2

Arcane Bullet

At 3rd Level you have learned to engrave spells into bullets and add material components to the powder charge in a way that allows firing the bullet to cast the spell. You gain proficiency with Tinkers Tools which you need on hand to craft your Arcane Bullets. You can craft Arcane Bullets in a short or long rest, you can maintain a number of bullets containing spell levels as indicated on the Arcane bullet list. Each Arcane Bullet contains the spell cast when it is created. All consumed Material Components are consumed when the Arcane Bullet is crafted, all somatic and verbal components must be expressed when creating the bullet as well. If a bullet requires a non-consumed Material Component with a gold value, this item must be integrated into your weapon with a tinker tools check with a DC equal to 10 plus the number of material components already integrated into the weapon.

For all spells the target is the impact point of the bullet when fired and range is the range of the firearm. Spells that have a Spell Attack Roll replace this feature with the Weapon Attack Roll of the firearm being used. Spellcasting DC is equal to 8+Ranged Attack Bonus. The spell replaces the standard weapon damage.

Arcane Bullets are loaded as part of the attack action they are fired and ignore the loading quality of a firearm.

Ricochet

At 7th level, you learn how to ensure a missed shot is not wasted, you can ricochet a shot to another target. When you make an attack roll with an arcane bullet and miss, you can use a bonus action to reroll the attack roll against a different target within 60 feet of the original target.

Adaptable Shot

At 7th level, you gain the ability to infuse your normal bullets with magic as they are fired. Any normal bullet you fire counts as magic for the purpose of overcoming damage resistance.

Elemental Shot

At 10th level you have learned how to infuse the power of the elements into your normal bullets. You can during a short or long rest change the damage type of your Adaptable Shot to: Fire, Acid, Lightning, Thunder, Cold or return it to Piercing.

Snap Shot

At 15th level you have gained mastery of your weapon, you can fire a shot intended to make an enemy flinch or seek cover. As a reaction when a creature succeeds on an attack or saving throw within range of an equipped firearm, you can force them to reroll and keep the new roll.

Caster Shell

At 18th level you are able to craft your Magnum Opus. During a long rest you can craft one Caster Shell. This is an advanced form of the Arcane Bullet. This bullet can be crafted to contain: Circle of Death, Disintegrate, Harm, or Gravity Fissure. This bullet is so volatile that it will disintegrate at the start of your next long rest from the arcane powers contained within. (Gravity Fissure originates at the barrel of the firearm when fired)

Spell List

1st	2nd	3rd
Chaos Bolt Chromatic Orb Dissonant Whispers Grease Guiding Bolt Ice Knife Inflict Wounds Magic Missile Magnify Gravity Ray of Sickness	Blindness/Deafness Knock Melf's Acid Arrow Pyrotechnics Scorching Ray Shatter Snilloc's Snowball Storm Tasha's Mind Whip Wither and Bloom	Daylight Erupting Earth Fireball Life Transference Tidal Wave

4th	5th
Blight Gravity Sinkhole Ice Storm Raulothim's Psychic Lance Vitriolic Sphere	Conjure Volley Flame Strike Negative Energy Flood Synaptic Static

Answer 1

A good start, but there are issues

This subclass is a pretty decent start for a new homebrew. The idea and thematics are solid. However, some of the mechanics need a bit of work. I'm going to mostly compare this to the Eldritch Knight and the unofficial Gunslinger fighter subclasses, as they the closest existing content.

Firearm Rules and Proficiency

It seems you are using the RAW firearms rules. That's fine, but most people find them overpowered and a strict improvement over standard weapons. Matt Mercer's Gunslinger subclass provides a pretty solid alternative ruleset for them. You would need to provide proficiency as well, but that's not a major issue.

Broken Spell Progression

There are multiple issues with the spell progression you have implemented. Unfortunately, all of them are overpowered.

1. Subclasses aren't 1/2 casters. You state you want to follow 1/2 caster progression. However, this is a subclass. No other subclass gets this kind of progression, only Paladin, Ranger and Artificer are 1/2 casters. The equivalent caster subclasses (i.e. Eldritch Knight, Arcance Trickster) are 1/3 casters, meaning they progress slower and don't get access to 5th level spells at all.
2. Nobody gets more than four 1st level spells. No caster in 5e, 1/3, 1/2 or even full caster gets more than four 1st level spells at any level. You currently get 11. This is completely broken.
3. It's unclear how spells are learned. You haven't indicated how a Gun Mage learns new spells or how many they have access to. Whether they have access to their entire list or just a selected subset greatly changes the versatility and power of the subclass.

I strongly suggest you change your progression to match that of the Eldritch Knight. If you do, it will solve all of the listed issues above. It will give you (1) a progression of Spells Known, (2) correct spells per level and also (3) grants cantrips. Overall, adopting the progression of other casting subclasses is the best way to make sure your subclass fits the game.

Arcane Bullet

This is the base feature of your entire subclass and is understandably a big part of it. However, there are still problems with it.

1. Crafting bullets on a short/long rest is a interesting way to prepare spells. It effectively locks the Gun Mage into choosing how they spend their spells ahead of time, which is unique in 5th edition D&D. This is not necessarily a problem.
2. There is no limit on how many you can craft per rest, just a limit in total number currently crafted. This means that the Gun Mage can burn through all their Arcane Bullets every short rest. This is a big problem. You are effectively giving a full 1/2 caster's amount of spell slots per short rest with easy recovery. You should either make this only on long rests, or find another method of limiting the number they can craft. (E.g. They can craft a number per short/long rest equal to proficiency modifier up to a maximum of Fighter level at any one time).
3. Tinkering into the weapon is a cool mechanic, but can be easily bypassed. You can just have multiple weapons to spread the components out. Also, there aren't that many spells with material components, so may feel like unnecessary bookkeeping. Consider dropping this requirement.
4. Guns have a much longer range than most spells. Inscribed bullets is an overpowered change, as it lets you cast spells that have a normally limited range over extended distances. You should consider limiting spells to their normal range.
5. Spellcasting DC is broken. By making the spell-casting DC equal to 8 + Ranged Attack Bonus, you are scaling the DC based on their primary attack ability. That means this character has no reason to invest points into anything other than dexterity, which determines their AC, Attack Rolls, and Spell saves. Consider making this based on Intelligence instead.
6. "The spell replaces the standard weapon damage." This is probably good from a balance perspective, but not that fun for the player. Delivering spells via bullets should feel awesome. Doing less damage than using a normal bullet doesn't achieve that. I have no suggestion since it might be overpowered otherwise, but this is just something to think about.
7. "Arcane Bullets are loaded as part of the attack action they are fired and ignore the loading quality of a firearm." Very very broken. By making the 'shooting' a part of the attack action, you allow the Gun Mage to use multiple per turn. At 20th level, this subclass could cast 8 spells in a turn by using action surge. Change this rule to be instead of the attack action, require a bonus action, or only be able to use one bullet per turn.

The arcane bullet feature needs a lot of work. What you are trying to do is difficult to balance into the 5e design philosophy. However, I suggest you look at the Gunslinger and Arcane Archer subclasses and draw some inspiration from there. (Self plug alert) You might also like to look at my Enforcer homebrew class for an alternative take on what you're doing here.

Ricochet

Cool feature, but you need to limit the number of uses. Proficiency or intelligence modifier per long rest seems reasonable.

Adaptable Shot

Reasonable feature for the level, but combined it with Ricochet and you are doing a lot more at 7th level compared to other Fighter subclasses. (Also, I don't understand how Adaptable = Magic? I would rename this feature.) Additionally, most fighters will have a magic weapon by 7th level, making this largely pointless.

Elemental Shot

Why make this restricted to a rest to change it? If you want it to be difficult to change it in combat, make it take 1 minute. Otherwise, just let them decide when firing. It's not overpowered, since Way of the Ascendant Dragon monk can do this from 3rd level. My suggestion is to combine this and Adaptable Shot into a single feature at 10th level.

Snap Shot

Another nice feature that needs some limitations on number of uses. Again, Proficiency or intelligence modifier per long rest is a good place to start.

Caster Shell

One casting of a higher level spell per day as an 18th level feature seems reasonable to me. It's not quite in line with what other Fighter subclasses get, but its not really broken either.

Conclusion

Overall, this class is extremely overpowered, but mostly due to problems with spell progression and the specific mechanics around Arcane Bullet. Fix up those things and you have a decent start for a homebrew subclass.

Answer 2

This is balanced.

Weaker than the battlemaster or echo knight, competitive with other fighter subclasses.

Presuming, of course, that you meant that bullets can be crafted after any short or long rest but still use up spell slots when crafted as per normal for spellcasting. If they get all their spells every short rest the subclass is likely stronger than its peers.

Ricochet is a bit odd in that it effectively gives advantage to every single magical shot. That's pretty strong but having to use that advantage to attack a different, perhaps unideal target (the mook instead of the boss say) is a drawback. It's a bit weird thematically, as ricochet shot usually means someone ricochets a bullet around a corner or something. Not misses, and then wills the bullet onto some other target. I'd just use this ability to mean that proficiency bonus times per day you can ignore Cover when firing at an enemy with a magical bullet.

Likewise, you note in comments that the spell table is incorrect and you meant to use a more typical one (without 11 1st level spells). Honestly, at level 15+, having a bunch of 1st level spells that cannot be used for absorb elements or shield is not a big deal. Like.. it is NOT a big deal. A fighter's typical gun attacks are gonna poop all over 1st level Chromatic Orb, at 15th level. Basically irrelevant.

The only remaining issue is that the last line of Arcane Bullet vaguely implies that you fire arcane bullets (aka, cast the spell) as part of an Attack action. That's not how it should work, or, how I assume you intend it to work. Firing a magic bullet should be an Action. Full stop. Not an attack or anything like that, as otherwise you end up with your Gun Mage shooting off 3 fireballs using his Extra Attacks and then Action Surging to shoot off another 3 fireballs, which is likely far too strong. Even shooting a spell and then also getting your second (or third) attack(s) would vastly increase the power of the subclass.

Finally, the abilities after Arcane Bullet don't seem much to fit with the theme of the class. They are gunslinger abilities, not gun mage abilities. Why not provide the ability to attempt to 'shoot down' incoming spells as a reaction, at level 15? Why not give them the ability to sacrifice spell slots to infuse their weapon with magic, at level 7? Why not let them mix a 1st level spell into their Extra Attacks at level 9, like the Bladesinger? You know, mage + gun things, not just gun things.