Guns

Guns came to prominence in the middle of the war when prototypes stopped exploding. There are several types, cartridge weapons, battery or zebra weapons, and projectile weapons.
Cartridge weapons work by harvesting the latent power of gems they fire bolts of force or made of pure elemental power. However they don't permanently drain the gem allowing effectively infinite round to be fired as long as one doesn't break the weapon. These have lower damage that the other types and must recharge every few shots but they don't need to be reloaded meaning they can outlast any other weapon and the troops don't have to waste space on ammo.
Zebra weapons permanently drain the gems and always fire elemental projectiles. These are significantly more powerful that cartridge weapons but require the user to carry around a large supply of ammo of find themselves weaponless.
Lastly projectile weapons are the most powerful but usually only fire one round before needing to be reloaded. However these weapons often only need to be fired once due to the immense amount of damage they can deal, or aren't meant for combat. Examples include mini-core launchers, Grapple rifles, coil guns, and syringe rifles.

Utility

These were used to fight with greatly increased efficiency. While zebra used spells and crossbows earth snipers could eliminate their casters without being noticed, pegasi could strafe from above, and unicorns could wield several weapons leaving a swath of destruction in their wake. Gryphons used exclusively melee attacks meaning even a single armed pony outmatched could pick them off long before they could harm the target. Dragons were the only real threat, and even then only the largest could stand against an battalion armed with these.

Manufacturing

A forge, the right gems, a smith who knows what they're doing, and the right ingredients. A master smith can make up to 2 guns a day on their own.

Inventor(s)

Unknown

Access & Availability

Initially they were military exclusive, but as territory was reclaimed and foundries established they were produced faster than troops could be trained. This allowed civilians to begin purchasing stripped down versions of the military weapons for self defense should the enemy attack their settlement, which was a disappointingly common event. These saved Equestria and thousands of lives in an exceedingly short time.

Complexity

On the surface the weapon is quiet simple. A common academical mixture activates a gem that is then carved to the proper shape and slotted into the weapon. The weapon causes a sudden burst of energy from the gem when the trigger is pulled, creating a projectile known as a bullet. In truth there is little to it besides a series of magic points at the right spots in the weapon that when they impact the gem cause and direct the energy burst.

Discovery

These were discovered near the midpoint of the war. The prototype was akin to a flare launcher and was intended to be used by those travelling in the mountains to start fires or signal for help. With some modification they became potent weapons of war.