Incendiary Bullets igniting objects.

I am making a shotgun with incendiary bullets and I have a question.

How do you use bullet.Callback to ignite the object with which the bullet has hit?

Or, is there an effect callback that I can use to ignite objects with which the effect has hit? ( made my own tracer so this would be preferred )

EDIT:

the tracer (sorry if blurry):

[lua]
bullet.Callback = function( attacker, tr, dmg )
local e = tr.Entity
if ValidEntity( e ) then e:Ignite( 10, 0 ) end
end[/lua]

ah thanks, will test out.

EDIT:

Works