Please find attached a end of the war summary from 6-Group concerning the ammunition used. By February, 1945, 6-Group had abandoned tracer ammunition. Did some crews continue to use it? I don't know, but they couldn't just choose: the Base or Station or Squadron Gunnery Leader would have to sign off on it. To Quote: " An interesting policy change was introduced in February, 1945, when the decision was made to abandon the use of tracer ammunition. The value of tracer ammunition had long been doubted, although it was difficult to obtain any agreement among gunners on its value. The introduction of the Gyro Gun Sight was perhaps the deciding factor in the decision to abandon its use. With the abandonment of tracer ammunition, loads were made up of 70% Amour Piercing and 30% Incendiary in the case of .303' ammunition and 100% Armour Piercing in the case of .50' ammunition. The last few days of the war in Europe saw another change in policy when Bomber Command instructed that future .303" ammunition loads were to consist of 100% Incendiary ammunition."
Note that Group Headquarters routinely had meetings that would have included section leaders to debate and go around on decision such as these. "Operations Research Section" (ORS) would also have been involved in these decisions.
Jim