"How else am I supposed to supply an illegal arms trade?"

This is the optimized path for completing the iron run.

Introduction

The iron run consists of collecting iron, processing it into iron ingots, and selling the finished product to the iron trader. Being a legal run, this run will not get you into any trouble with the Altis police and is eligible for speed and profit bonuses when doing this run with a Worker's Protection License (WPL).

Starting the Run

Before starting this run, it is strongly recommended to check the price of iron for optimal profits and to follow the list below to make sure you have all the required equipment.

A pickaxe (Purchased at gas stations/markets) Required for collecting iron
Food & Water
Bergen Backpack for space
A large vehicle to store the most iron
Iron processing license ($9,500 at the DMV)
Head to the iron Mine south of Agios Dionysios to fill your vehicle and optionally your backpack using left windows key in the iron mine area.

Processing

Head slightly southeast of the iron mine to the iron processor to refine your goods into iron ingots
To process, scroll wheel on the Processor NPC underneath the overhang, you can either process from the vehicle or from your backpack and must remain 25m of the NPC.
Before pressing Process, it will give you the time required to process. Canceling processing will process items up to the progress you obtained

Selling

After finishing processing take your vehicle to the iron trader east of DP12
Scroll wheel on the iron trader to sell your iron ingots on your person, you will need to manually remove the ingots from the vehicle to sell
When finished selling go to any ATM the closest being DP12 to store the money via scroll wheel or left windows key on the ATM

Payout

Using a box truck equipped with a tier 4 turbo and a bergen backpack, this run takes approximately 26.5 minutes to complete starting from the nearest truck shop to the moment the iron ingots are sold.
Traveling to the nearest ATM and storing your $367,920 will add an extra minute to the run's time.
Using a Worker's Protection License (WPL) during this run would increase your profit to $423,108.