A spell needs more than just the power you put into it to work. You need to justify how that power works. Against guns, it is really easy; 5 shifts of intentional hexing can break most automatic/modern firearms, 7 shifts of hexing can break up to late 19th-century technology. Add 2 shifts for zone-wide and guns, grenades, spy/police/military gadgets, tazers, stunners and all that are gone.
Disarming is done as a maneuver. The effect strength has to be at least 3 or the opponent's relevant defense, whichever is higher for the maneuver to work. So if they got a might of 6 and you're trying to disarm them, then your spell needs a base strength of 6. Ideally, you go for spell types that work against the lowest defense.
To disarm metal weapons like swords and the like, remember that scene from Lord of the Rings and also recall that metal can heat up real well. Use fire (or extreme cold) to justify a disarm of the spell's strength vs Endurance then add 2 shifts for zone-wide. If you are feeling vindictive, add a couple of shifts for duration so if they try to pick up the weapon again while the spell lasts, they realize it is still extremely cold/hot.
Use magnetic pull to justify disarming vs Might. Extra duration does not make sense but extra shifts to throw the weapons several zones further do.
Electricity for the Air element works just as well as fire.
Water is the element of entropy. So to disarm, justify it as a moment of extremely bad luck so they somehow trip up on their own weapons and drop them; a disarm against athletics.
Spirit could disarm with main force (vs Might) or you could "command" them to drop their weapons with subtler mind magic (vs Discipline). Though the latter could be Lawbreaking.
To destroy weapons, you got a big problem. If you make zone-wide spells, how do you target only the weapons and not their wielders or the surrounding objects? The disarming works as zone-wide because the effect would be irrelevant against targets that aren't weapons. But a straight attack might work on everything; try to break weapons zone-wide with main force and you might break their wielders too. To justify a zone-wide attack only working on the weapons, use some effect that would only affect them.
Magnetic force to tear them apart would affect the weapons - and other nearby metal items. Weapons are fairly fragile - even human strength could break a sword or axe if it was swung too hard for too long and firearms are easier to damage. So a strength 6 might effect (plus zone-wide) will break most metal weaponry without breaking bigger, sturdier metal objects.
Heat to melt them or cold to shatter them, again working only on metal. Strength needed to do it would be similar but the damage potential to other metal objects nearby is a bit higher.
Pure force does not work; it would affect everything in the zone (which would be bad)
A rust attack via entropy works just as well as heat or cold.