Do Pyros have any fire resistance?

Solution 1:

Most weapons in TF2 have min\max damage. So no, Pyro does not have any resistance beyond immunity to afterburn if you take him with base stats. Some gear provide reduction of damage to certain elements, such as fire and explosives, so that can affect your overall damage output as well.

Also, some weapons have damage based on where you hit, such as a headshot is a lot more damage than a body shot for example. The ambassador comes to mind as it's guaranteed crit on headshot.

The detonator projectile deals 10-20 base damage, so that explains why you see "only" 11 damage dealt at times. Here is the TF2 wiki site for that weapon: https://wiki.teamfortress.com/wiki/Detonator