SAM Ammo is the only ammunition type for the SAM Site, an anti-air base defense turret. RUST initially integrated this ammunition type to combat flying vehicles such as minicopters, scrap transport helicopters, and hot air balloons from entering the space around the SAM site, typically large player compounds.
Most notably, the Launch Site monument boasts several SAM sites with unlimited ammo to stop players with these crafts from flying to the top of the monument unchecked and claiming the loot found there.
Players may only acquire SAM ammo through purchase (and potential research) from the Outpost monument. They can also invest considerable scrap into the Tier 2 Workbench to research and craft it.
With the coming of the November 4th, 2021 Abandoned Military Base patch, SAM ammo is quickly becoming a much more defensive necessity for targeting and shooting down incoming MLRS Rockets. It is estimated to take three loaded SAM sites to entirely shoot down a whole barrage of 12 of these MLRS rockets.