Fortunately, Reaver, SR5's Hard Targets abstracts hand loading ammunition, even exotic kinds like Stick-n-Shock and Depleted Uranium (assuming you can find the raw materials, of course) into a single extended test with a fixed difficulty. Thus, you don't really need to think about real-world implications of what you're trying to accomplish, which, once again, you seem to get hung up on a lot, and just roll the dice until you hit the threshold (or not).
Let's take an example from Hard Targets. To craft ammo you need an Extended Armorer test, with the threshold and interval to craft 10 rounds listed on page 189. The table breaks ALL ammunition types into 4 simple categories; regular and special firearms ammo, and regular and special heavy weapons ammo. The threshold for the two former is 4 and 6 respectively with an interval of 30 minutes, while for the two latter it's 8 and 10 respectively with an interval of 1 hour. You need a Hand Loading tool kit and crafting materials costing the normal value of the ammunition +10%.
Thus, crafting 100 rounds of regular ammo for your Heavy Pistol would be 10 Extended Armorer tests, each with a threshold of 4 and a duration of 30 minutes. A semi-skilled PC with Logic 4, Armorer 4, and a specialty in Hand Loading rolls 10 dice, and will average 4 hits on two tests, which means it'll usually take him 10 hours to hand load 100 rounds of regular ammunition, and each 10 can get either +1 DV or -1 AP.
Extrapolating this to arrows is dead easy as far as my table is concerned. You break arrows into the same two categories (i.e. normal and special), and use all the same rules. If you want to make it more granular you could make it so that the arrow Rating comes into play, so make the interval (Rating * 3) minutes for the same general 30 minute interval for example.
Thus, a character wanting to craft 10x Rating 10 normal arrows needs 4 hits on an Extended Logic + Armorer (4, (10*3) minutes) test. Job's a good'n, no need to make it more complicated unless you as a GM feel it's warranted...