An old friend of mine (WO Walt R******t) was a WOp on 12(B) Sqn Lancs from Dec 44 - Apr 45. He told me that their Mid Upper Gunner made his own 'mix' of ball to tracer. He reckoned the normal mix was '4BIT' = '4xBall, 1 x Tracer', but he said that his MUG's preference was '1BIT' = 1xBall, 1xTracer, and said that when the gunner opened up it was like Blackpool illuminations. But what Walt did say was that the combination of this light show, combined with the gunner's accuracy kept them safe form the attentions of the Luftwaffe.
However, the downside was that the same MUG shot down his own Lanc on 27 Feb 45!!! They were airborne on an air-to-air firing duty, and when the Mid-Upper Gunner was firing, the guns 'stuck' on 'fire'. The gunner jumped down to break the links, but, not only did the guns continue to fire, but the turret also continued to rotate, and, to add insult to injury, the interrupter gear failed to work. So the 1BIT raked the port wing from leading edge to trailing edge causing the wing to catch fire. The pilot ordered the crew to bail out, but he managed to land safely!!!
Sounds unlikely, and a bit of a 'line shoot', but, after his death, I was left Walt's medals, his Caterpillar Club badge, his Caterpillar Club 'certificate, and his Log Book. And the entry for 27 Feb 45 simply states (and no 'I'm a [bloody] Celebrity...' style histrionics here):
Date - 27/2/45; A/C - "J"; Pilot - F/O Large; Crew Duty - W/Op; Duty - Air to Air Firing (Port Mainplane on Fire - Bailed Out). Skipper Landed A/C; Hrs (Day) - 0:50