1. Start a new single player game master match.
2. Place a Soviet weapon arsenal and any player character.
3. Place an Mi-8.
4. Take control of player character.
5. From the arsenal, grab an SVD and magazines loaded with tracers.
6. Equip SVD and reload it with tracer rounds.
7. Fire one round away from the Mi-8, so as to remove the chambered round.
8. Fire at the Mi-8 fuel tank until a fire is set.
9. Return to game master, extinguish fire and repair Mi-8 .
10. Repeat steps 4-8, substituting tracer magazines with API magazines. Note that the fire consistently takes longer to start.

This can also be reproduced with UH-1H helicopters, at least.

On the other hand, the results line up with the expected damage values when shooting at some targets. For example, reproducing this by shooting the fuel tank on the American M923A1 transport truck results in a fire starting significantly faster with API rounds than tracers.