• Make 100 science packs or ammo mags, and a container.
• Use one of the science packs or ammo mags until it's at 10% durability.
• Place the 99.1 science packs / ammo plus a container into a containerization machine to get a container of 100x the item.
• Unpack it to produce 100 items with full durability plus the container.

Not sure how hard this would be to automate, would probably need a timer or something because I don't think you can read an item's remaining durability with circuit network.

I don't think there's any way to fix this, except forbidding packing for ammo and tools entirely, which IMO isn't worth it.

The base game also has something like this - you can use a yellow mag to 10% durability, then turn it into a red mag, then use that to 10% durability, then turn it into a uranium mag. But it's not cyclic like container packing/unpacking so it doesn't allow infinite free stuff.