They do work. We shot many cases of surplus red paper Rem. hi-base (copper not brass) 8's when I was at Quantico in '56-57 shooting skeet. I shot with a Parkerized Savage copy of the Rem. Model 11 with a Cutt's Copmpensator. Cartridges came in boxes of ten. Had a heavy little cup of red tracer comp in the top wad that stayed with the shot well, as occasionally the cup would hit a clay. They did start a few fires though when a burning cup landed among target debris in dry vegetation. Still the best coaching came if a person could get behind the shooter and watch. Raised a few eyebrows when I took a bunch home and used them on the duck pass.
