Try using the repeat command like this
local inst = mc.mcGetInstance()
repeat
local ActualTool = wx.wxGetNumberFromUser("What tool is in the turret?", "Tool # ","Current Tool", 1, 1, 6) -- Default, Min, Max.
until ActualTool ~= -1
--mc.mcToolSetCurrent(inst, ActualTool)
wx.wxMessageBox(tostring(ActualTool))
DazTheGas