Firstly, this upset me, as the GM of our current Iron Gods AP, to hear that not only what was supposed to be a spectacular and world building piece of loot was nerfed beyond desire, but also that a player has invested a level dip into a piece of gear, and after doing slightly above average damage for a 10th-level character, was rewarded with a revision of his stats. That's just really sad, but as far as RAW goes, this took me a couple of minutes before I could come up with anything to say. Number 1, if you're indeed using an arc rifle, then no problem, it doesn't have the semi-auto property, but in fact, the automatic property, enabling you to make a cone attack with every single attack in the round. On the other hand, if you meant arc pistol, then it is semi-auto. It is hard to see, just by looking at the description of semi-auto weapons, how to make a case for getting your iterative attacks, however, Paizo doesn't make a habit of redundancies, and when they do, they typically specify that it is for your convenience and not a special case. What that means is that the fact that Slow-Firing weapons are described as requiring a full-round action to use, and that "cannot be used to make iterative attacks" is included in the description, means that Slow-Firing weapons are an exception to the normal iterative attack rules, and the lack of the Slow-Firing property on the semi-auto weapons is intended, and as such are specifically excluded from the weapons that are unable to make iterative attacks. If semi-auto weapons were not intended to be capable of iterative attacks, then Paizo would not have created a weapon category to mean specifically that, and then not included it in the weapon's description.
