So with the patch many people can no longer restock on ammo doing the violent duct mission.

There is way to buy ammo and armor but still be able to repeat the mission over and over as many times you want

Each time you restart the mission, play through until all of the bikers are dead. Dont deliver the coke right away. Go on your map and find the ammunation right next to the deal location. go in and you can shop from it like you would normally. That is how you can resupply without leaving the mission.