Actually, the British planes the carried the DeWilde bullets didn't leave a tracer trail either.
The DeWilde, as I understand it was not a 'tracer' round but a 'sparker' round that provided a bright flash when it hit something. (If anybody knows more about it, and can correct me on this, I'd appreciate it

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This would give you great feedback on hits, without giving away the fact that you're shooting! Excellent for low six bounces

finn