What makes a weapon "magic"?
People really belived that some weapons were magical(some still do),
what is required of a weapon before it can be considered magic?
If you rule out the those who have aquired a certain amount of fame because they belonged to someone legendary like Hitler or Julius.
It could be the materials it was made of, method of production, producers, decoration, consecration, possesion, accumulation of power, ritual function, martial practise.
Many traditional weapons are said to derive power from having been made of sacred materials. Such materials in their natural state have affinity with the divine, so objects made from them are themselves sacred. Examples: Keris blades of the Indonesian archipelago made from meteorite iron, thought to have been sent by the gods; rhinoceros horns as hilts for Arabian janbiyya, believed to have healing and aphrodisiac properties.
Method of Production
The act of making a weapon itself -- particularly the forging process for metal bladed weapons -- is thought to be a magical process, transmuting the essential nature of the materials such that they acquire new properties not found in their natural state. We find this often taking place in a forging environment where the production is encoded in ritual processes. Example: The forging of Japanese
katana blades, in which the smith dons a priest's robes and makes numerous invocation to Shinto dieties.
We also often find that the method of production creates a visible pattern in the finished product, which is itself given specific supernatural attributes. Examples: Hamon on Japanese katana, pamor on keris, wootz patterns on Persian shamshir.
Many cultures regarded weaponmakers and blacksmiths to be imbued with magical power through their craft; their objects therefore inherit some of that power. Examples: Viking swords; West African swords.
Empowering weapons through the application of spiritually significant artwork. This is very common throughout history, with everything from full figural artwork (Example: Keris hilts from Bali) to talimanic markings (Example: Beduh magic squares on Middle Eastern swords) to prayers and religious inscriptions (Example: Biblical and other Christian mottoes on European swords).
There are a number of cases in which the original meaning of such decoration is lost but the practice remains. Examples: Cho on Nepali khukuri; ganja on keris; swivels on Hindustani sword and dagger pommels.
In other cases certain decorative objects thought to impart power are added. Examples: Boar's tusks on Nias balato scabbards; tiger jaws to Kachin ninjthu; gemstones on various European daggers.
With a few rare examples, the overall shape of the weapon itself is thought to be talismanic, eg. the Achinese rencong, believed to spell out the Islamic Arabic invocation bismillah 'in the name of God'.
Making weapons sacred through the blessing of ritual specialists. Example: Hindustani weapons undergoing shastra-puja; Siamese weapons in krabi-krabong practice.
Many cultures had rituals to animate weapons, calling spirits or other entities to reside in the weapons themselves. Examples: Hantu residing in keris.
Accumulation of Power
Some weapons were thought to absorb the strength and heroism of their previous owners, and impart those virtures onto their present owners. Examples: Viking and Medieval European swords. Others could be used to extend and focus a user's personal energy to cultivate spiritual awareness. Example: Chinese jian in Taijiquan and other internal martial arts.
Certain weapons are considered powerful because they are implements in specific rituals. Examples: Tomahawk peace pipes among many Native American tribes; sacrificial knives of all kinds; fraternal swords in Europe and America.
For some, ordinary weapons can take on ritual importance through the practice of marital arts, which foster altered states of spiritual consciousness. Examples: Bolos in certain Filipino martial arts; rapiers and swords in certain Renaissance schools of fencing.