With 6 PD and without looms, you're looking at between 3 and 12 barbed arrows (5 if you hit for average damage every time) to kill a 50 armor target with 70 HP (21/18 7 IF), assuming a point blank shot with no speed bonus (and no headshot, obviously).
If you really want to do that, go 18/18 with 150 bow WPF and 60 1h WPF (or 21/15 with 140/60). You would probably be better off hybridizing with a crossbow or throwing build, however.