Bought .223 tracer's some yrs back. Bought them from Sportsmanguide or Cheaperthandirt? Maybe both, don't recall exactly. Only reason I bought them or used them. Was visually watching bullet drop & wind drift @ varying yardages. Definately, helped my skill on shooting running coyotes, as for lead time /ubbthreads/images/graemlins/grin.gif.
Also used them in my old .308FN/FAL, while T-shooting. Loved that old thumper.
When we were young. We could buy .22 cal tracer rds @ our local Army Surplus. Don't recall their bullet speed back in those days. but reminded me of watching a BB come out of an old Daisy rifle. Looked mighty slow.