I use 2.5 oz per gal. Using spray grade is the best so you don't have fillers, binders, or dirt. I'm just cheap so I use the AMS which isn't spray grade. At $35 for a 50 lbs bag, I fert the lawn with it and use it in my sprays. On occasion, I'll get clogging of the sprayer but I'm not sure if there was dirt which fell into the sprayer or if it was in the AMS. As granules, you do have to agitate it more to dissolve it. Spray grade generally comes in a more powered form or fine salt like granules and is more pure. If you use AMS to fert in early spring and late fall anyway, then you already have it...
Regarding AMS and herbicides, if you are interested in reading it, I'll post up the research on it. Otherwise, I just use it with pretty much everything I spray. If you haven't already, check the PH of your tap water and then add your 2.5 oz AMS/1 gal to it and recheck the PH. It should be between 5-6 if your water was around 7. If you have alkaline water, you can add citric acid to lower it even more. (You only really need to do this the first time since your water supply probably doesn't change ph. Now you know the rates for the future.) The acidic solution will increase penetration. Keep in mind, the herbicide can also lower the PH of your solution. I always combine it with NIS or some other surfactant so you have 3 additional things to help increase the effectiveness of your chosen herbicide. N source to increase growth and aid absorption, surfactant to reduce runoff and increase leaf coverage, and acid for penetration. I like to add my mix in this order: AMS, mix, herbicide, mix, test and use citric acid if needed, surfactant (and dye if you want). As a note, for iron, I add AMS, citric acid, check ph, then add the iron last as the citric acid should be in solution to chelate the iron but that isn't the case with herbicides.