Hey HWC! thank you! glad that you liked the supplement. In response to your questions, as per the survival guide, I understand that reload takes an action, then players can move as well, but in the case of the Sunless king, reload takes movement as well. The full turn should be spent standing in one place changing magazines. Shotgun shells only, is just so people know that you cannot use smart rifle ammo in a shotgun! So for a shotgun, you could go normal, which is shooting with the guns damage without any additional effect, or custom ammo of the shotgun category. For railguns, notice that there are just 2 railgun custom ammo, and thats all they can use, plus normal which will be just railgun damage in the stat block.
Let me know if you have any other questions!