I have installed betterloot and edited the loot table - each time using the Oxide.reload command to reupload the plugin and thus the loot table to the server - doing so after editing the Scrap per container is working fine ( changing the scrap value from 10  - 100 - 10 and updating each time is working. 

However for some reason my Min and Max items is not working on anything and will sometimes only spawn the scrap, sometimes 3 items sometimes more. 

Are you unloading the plugin before editing the Data loot table , then saving, then reloading ?
Have you checked your edited json with a validator to make sure there are no missing , } ?