How to lower a NumValue everytime a function is called?

The code below makes it so that every time the cannon is fired, the number value goes down by one and once it reaches 0, the cannon has to be resupplied. The problem is that every time the function is called, nothing happens to the number value.

repeat wait() until script.Parent.Parent.Vehicle.Value~=nil

db=false
held=false

v=script.Parent.Parent.Vehicle
f=script.Parent
missile=script.Parent.HE
f=script.Parent
bin=script.Parent

function fireguns()
v1=v.Value.Gun1Bullet:clone()
vel=Instance.new("BodyVelocity")
vel.Parent=v1
v1.Velocity=v1.CFrame.lookVector*500
v1.BodyVelocity.maxForce=Vector3.new(4000, 0, 4000)
vel.velocity=v1.Velocity
v1.CanCollide=true
v1.Transparency=0
v1.Damage.Disabled=false
v1.Parent=workspace
end

function launchmissile()
v.Value.Effect.PointLight.Enabled = true
v.Value.Effect.Smoke.Enabled = true
v.Value.Missile.Fire.Enabled = true
v.Value.Effect.Light.Enabled = true
v.Value.Effect.Fire:Play()
v.Value.Effect.Transparency = .5
v.Value.WER2.Value.C0 = v.Value.WER2.Value.C0 - Vector3.new(0,0, .5)
v1=v.Value.Missile:clone()
v1.CFrame = v.Value.Missile.CFrame * CFrame.new(0, 0, -5)
vel=Instance.new("BodyVelocity")
vel.Parent=v1
v1.Velocity=v1.CFrame.lookVector*500
v1.BodyVelocity.maxForce=Vector3.new(4000, 0, 4000)
vel.velocity=v1.Velocity
v1.CanCollide=true
v1.Transparency= 0
v1.Heat.Disabled=false
v1.Parent=workspace
wait(.001)
v.Value.WER2.Value.C0 = v.Value.WER2.Value.C0 + Vector3.new(0,0, .1)
v.Value.Effect.Transparency = .6
wait(.001)
v.Value.WER2.Value.C0 = v.Value.WER2.Value.C0 + Vector3.new(0,0, .1)
v.Value.Effect.Transparency = .7
wait(.001)
v.Value.WER2.Value.C0 = v.Value.WER2.Value.C0 + Vector3.new(0,0, .1)
v.Value.Effect.Transparency = .8
wait(.001)
v.Value.WER2.Value.C0 = v.Value.WER2.Value.C0 + Vector3.new(0,0, .1)
v.Value.Effect.Transparency = .9
wait(.001)
v.Value.WER2.Value.C0 = v.Value.WER2.Value.C0 + Vector3.new(0,0, .1)
v.Value.Effect.Transparency = 1
v.Value.Effect.PointLight.Enabled = false
v.Value.Effect.Smoke.Enabled = false
v.Value.Missile.Fire.Enabled = false
v.Value.Effect.Light.Enabled = false
wait(.001)
end



function missileclick()
local ammo = bin.Munitions
ammo.Value = ammo.Value-1
f.Visible = false
print("click missile")
if db==true then return end
db=true
missile.Text="Reloading"
launchmissile()
v.Value.Effect.Reload:Play()
wait(4)
missile.Text="Fire HE"
v.Value.Effect.Reload:Stop()
db=false
f.Visible = true
end


function gunsdown()
held=true
while held==true do
fireguns()
wait()
end
end

function gunsup()
held=false
print("up")
end


missile.MouseButton1Click:connect(missileclick)
--sabot.MouseButton1Click:connect(sabotclick)
guns.MouseButton1Down:connect(gunsdown)
guns.MouseButton1Up:connect(gunsup)