Tracer Problem #1
To help pilots better target their shots, their guns had tracers loaded into the rounds. Tracers shone brightly enough to target even during daylight. The standard cadence for tracers is every fifth round in a machine gun belt. There was only one problem with this plan – tracers did not behave the same as bullets. If they were on target, the bullets would not be, so pilots had to adjust on the fly… as it were.
Tracer Problem #2
On top of the inaccuracy of tracers, there was another problem. Tracers clued everyone, including the enemy, into the location and status of the pilot. Adding to that, when a round ended, the pilot would fire multiple tracers, letting everyone know he was out of bullets. Pilots who refused to use tracer rounds, reportedly, had greater accuracy and evaded the enemy better.