In the Savage Worlds Deluxe Explorer's Edition rulebook, page 54 says:
Auto: This full-auto weapon may fire in automatic (single-shot) mode.
Page 55 says:
Rate of Fire: This is the maximum number of shots that may be taken by this weapon per action. Unless a weapon says otherwise, the user can fire up to the Weapon's Rate of Fire (rather than its full Rate of Fire). If a single shot is taken, it uses a single round of ammunition and does not incur any recoil penalties. Two or more shots with such weapons always incur the -2 autofire penalty.
Page 79 says, under "Automatic Fire":
Full-Auto and Ammo:
[...] each die rolled on full-auto represents a number of bullets equal to the weapon's Rate of Fire when counting ammo, even though only one "bullet" can hit and cause damage from that die. Firing all three dice with a Thompson gun (Rate of Fire 3), for example, consumes 9 bullets.
Most automatic weapons can be set to fire full-auto or single shot. If a weapon has selectable automatic use (Auto), you can fire a single shot (and also ignore the full-auto penalty of -2).
These rules seem to conflict a little. The Rate of Fire description says that all automatic weapons can fire in single-shot mode unless specifically noted otherwise. Pages 54 and 78 seem to imply that while any weapon with RoF >= 2 can fire in automatic mode, such weapons are only capable of firing single shots if they also have the "Auto" note (which is a little counter-intuitive!)
Question 1: Can a weapon with a RoF of 2 or 3 without the Auto note (e.g. core book Gatling Gun) be fired in single-shot mode, or not?
Question 2: If a non-Auto weapon has a RoF of 3, what is the minimum number of shots that can be fired from it? 1 (with a -2 recoil penalty, and consuming 3 ammunition, because it's still "automatic" fire), or 2, or 3?
Question 3: What happens if there aren't enough bullets left in the magazine to satisfy the ammo requirement of the stated Rate of Fire? (e.g. there are only 5 bullets left in a RoF 3 weapon). What if you're attempting suppressive fire?