You've understood the ways of conjuring magical ammunition and artillery for a short period of time and enhancing already exicting.

Supply Savant

At 2nd level, You have optimized the amount of material components required to utilize certain spells. The gold cost for acquiring material components is halved.

Expanded Armory

From 2nd level, You gain proficiency with the following:

• Firearms
• Crossbows (Heavy)
• Shortbows
• Longbows

Abundance of Ammunition

Starting at 2nd level, you can use an action to summon either 5 x your spellcasting level magical arrows / crossbow bolts or 2 x your spellcasting level magical bullets. These deal an additional 1d6 Force damage. The ammunition disappears if you are unconscious, incapacitated or take a short or long rest. You can’t cast this again, until you’ve finished a short or long rest.

At higher levels. The damage die changes to a (d8) at 11th level, and a (d10) at 17th level.

Arcana Ballistics

From 6th level, you can use an action to conjure a medium sized cannon within 30 feet of you for 1 hour. The cannon does not need to be reloaded but will fire a magical cannonball up to 400 feet away, dealing 5d8 Force damage in a 10 ft. radius. All targets in the area, must make a dexterity saving throw against your spellcasting DC. If successful they take half, and if not they take the full amount.

The cannon is locked in place and cannot be moved along any axis, although it can be rotated and it counts as half cover for creatures you designate. It’s Hit points are equal to your Spellcasting level x 2 and it’s AC is equal to your Spellcasting DC.

It takes an action to aim and fire the cannon, and allies using it has to be within reach of it. You on the other hand, can remotely rotate and fire it from within 20 ft. of it. Only creatures that you allow to, can rotate and/or fire the cannon.

The cannon disappears prematurely if you become unconscious, incapacitated or take a short or long rest.
You can’t cast this again, until you’ve finished a long rest.

Ensorcelled Equipment

At 10th level, you can enhance up to 5 melee or ranged weapons with magical energy. These weapons now count as magical weapons if they didn’t before and deal an additional 2d6 Force damage. The weapons lose their enchantment and the feature resets after every short or long rest.

Siege Magic

Starting at 10th level, your cannon now deals Double damage to Constructs and Structures.

Additionally you may rotate and fire your cannon remotely, and its range increases to 800 ft.

Mons Meg

From 14th level, your Arcana Ballistics Cannon now deals 8d10 Force damage and counts as ¾ cover for targets you designate. Your control range extends to 200 ft.