Is this what I might know as Screw Your Neighbor, or something like that? If you can bust a chunk of the shooters target (easy if they whiff) they get eliminated?
I did a fair amount of trap before I started doing skeet, and went to a Turkey Shoot around the holidays at one club. The event was simply ten targets at the 16yd line, first place got a turkey, second place got a chicken. But tiebreakers were settled by backing up (I heard these shells also referred to as backup shells, and I think they meant back up) all the way back to the clubhouse, probably about what would be the 35yd line. As I am getting ready to shoot I notice a guy offering a shell to the guy I was shooting against, and since I was about to toss 1oz of #8 in a probably futile attempt I said something like "Hey, did you bring enough for everybody?!?!" The guy was a nice guy and gave me a couple of shells, 1/4oz of #5, the lag time was hilarious. Anyway, being dumb and impulsive the way I am I figure nothing like that better happen to me ever again, and in that quest loaded up some 1-1/2oz of #6 @1150 and bought eight pounds of Longshot in the process.
I soon figured out that was about seven and a half pounds more than I needed, so I was glad to see there was a lotta pistol data for it. I ended up using a bunch for 40, and a little for 45, now (IMO) it is working pretty well for 147g 9mm.
But those original 12g shells I loaded never got used for trap, but they have been coming in handy for three gun, the club I shoot at has some of the MGM spinners (jump to 2:55), I like to shoot the third shot on the back of the plate. They also make a double, the guys that are good get them both working at the same time, I screwed the pooch last month trying...