In the
Dwarf Rep spoiler near the bottom, you'll see the prices for gun runing is 5/10/15, with the difference being 1 rune, 2 runes, and 3 runes. Only the most simple runes can be used on gun runes, so no master runes. The only non-master rune that increases Initiative is the Rune of Speed, which increases Initiative by 1 per rune. It'd be 5 favours for one Rune of Speed, 10 favours for two, 15 favours for 3. As for dwarf/runesmith favour, I think you're wrong. I highly doubt we'll get
that much runesmith favour. As for dwarf favour, we only have 46. Spending 15 favours on a quick draw gun would wipe out a third of our dwarf favour right out, so you really can't be talking about dwarf favour being functionally bottomless.