There are quite a few old discussions on this, i apologize if people are tired of discussing this! I could not really find a good argument for playing it the way i currently do so here it goes.
If a unit is firing more than one shot with the Template type, resolve each shot, one at a time, as described above, determining and recording how many hits are scored by each template. Once the number of hits from all templates has been determined,roll to Wound as normal.
Flipped through the rulebook again, when reading the multiple template rule i realised i have been doing different templates wrong (rolling one at a time for different types). The method i have been using is accepted way in general (one at a time when mixed profiles) and i don't really want to start any arguments during a game regardless, but when searching different sites their seems to be a divide (most people going with do one at a time)
Since specific override general rules i'm having trouble seeing how you roll one template weapon at a time, this looks so clearly like you roll everything at once from my point of view. Why would the multiple template rule exists if not for this purpose? It's quite obvious how to resolve 2 identical flamers without needing a rule decribing multiple templates.
Edit: Typos