Machinegun skill? Seeing as how the number of zombies went dramatically up while their health went dramatically down in the 3D, I believe a low-mid level machinegun could help me. Maybe a Mesa ACR or something? What do you think, Umbrella?

Also, as a secondary question, if I have 100 accuracy, how accurate would an assault rifle be?

I say invest in a Grinder. If you already have one, invest in another.

But seriously though, go with machineguns regardless. I think all builds should include them. Not to mention that the best weapon in the game requires 100 machinegun skill.

As for your accuracy question, I don't really know.

Medium accuracy at 100 (Maybe 1 out of 3 shots will hit), but it depends on the range. Also, this is just me guessing.