I have been running through Veteran with this build.
First, the weapon you will be using for this is the shotgonne. The reason for this is twofold. The damage of the shotgonne is the highest of all ranged weapons. Wands and cannons are technically ranged, but they fall under magic and heavy weapons skill groups, respectively. The damage, as well as the arc, of the shotgonne is offset by its short range. Which brings us to the second reason, Rapid Fire has its own range independent of weapon range. Tier 2 Rapid Fire gives your shotgonne 12 yard range.
Now, your first thought will be that Rapid Fire has damage reduction to balance its fire rate increase. While this is true, Long Range Mastery can negate most of that penalty by the time both skills are maxed. That’s what makes this build so deadly. The final damage per shot from Rapid Fire is 68.9% less than an auto attack. After the armor reduction penalty is applied to your target, each shot of Rapid Fire can actually do more damage than an auto attack.
As you level, you will run into level restrictions. So where do we put these extra skillpoints? The first skill you go for is Shotgonne Mastery. It gives a stun, a blind, and knockback. Rapid Fire hits will proc all SM bonuses. Once you start putting points in here, not even bosses can touch you. Bosses may be immune to stuns and blinds, but they can still be knocked back. It’s around level 12 that this build starts geting OP.
The second skill you want to start pumping is Poison Burst. Since you are going pure Focus, it only makes sense to apply as much elemental damage as possible. Gem your shotgonnes! Your DPS will skyrocket. What makes Poison Burst have such amazing synergy with this Rapid Fire/Focus build is that Focus is a direct increase to the poison damage. Rapid Fire then strips armor from all categories from your target. Resistances mean nothing with this build.
Outlander 15/1/0 My level 13 build just before starting Act 2. The calculator says level 16 required, but I had 3 extra skill points from Fame. Packs fell like I was playing easy. Seriously, this is almost as OP as Embermage builds.
So, things will continue through Act 2 and your build should look a little similar to this. I had gained another 4 points from Fame by the end of Act 2. Look down at the attributes level requirement for the real level, which was 25 for me. The next skill I added was, of course, MoE. With just 2 points I increased the poison damage by 8% and my gemmed damage by 4%. The knockback bonuses could blow enemies nearly off the screen and take down champions within seconds.
I haven’t made it through my first full playthrough, but this will be my maxed build at level 100 and Fame 50.
The rest of the abilities are for nothing but CC. Bramble Wall, Vortex Hex, and Rune Vault all confer status effects, damage, and hinder movement. Shadowmantle is to enhance survivability and take out ranged atackers so I can focus on using Rapid Fire to keep melee enemies away.
This is a glass cannon(shotgonne?) build, but using the right equipment to increase armor and HP can give you just enough time to pop a potion and run away for the second or two that it will take to regen your health and wipe the floor with them.
I will update this once I get into NG+. I don’t see much changing, though. The synergy and gear scaling are beyond OP.