I'm sure you are aware of the 10% tolerance built into all model rocket motors. If not let me tell you that is quite a difference. Most of the time much of this margin is in the delay mixture, but also in the propellant grain as well. If you weigh your motors you'll usually find a good bit of range between like motors. In some motors this number can be several grams. When getting ready for a cluster altitude meet I will buy as many as 8 or 10 packs of the motors to be used. In a 6xC6 clu/alt event I went thru 18 3 packs of C6-0's matching as many of the heaviest booster motors as possibles to come up with 3 matched sets of 5 boosters and the heaviest C6-7 I could find. You never know how many flights it's going to take to get a closed track, or tracked at all for that matter. This one worked out very well. Tracked and closed on the first flight at 666m (2,185ft) a national record at the time
If using say 3 C6-5 motors in a model, you will always hear Pop, Pop, Pop at ejection. Most of this is the difference in the delay time of the motors, a tiny amount is due to difference in ignition time and the rest in extra propellant burn time. does this help, I think is does especially with booster motors as the heavier the motor means more propellant in those motors. "the racers Edge", possibly enough to make the difference between a nice flight and a national record
I'm not competing anymore because of a back and knee problem but I'm happy to pass along some of the BTC tricks of the trade.
You will need a good gram scale or triple beam balance to take full advantage of this process. If using a digital scale make sure it will tare out to 0g and read accurately to at least .01grams
this process works for all competitions regardless of power class, but is most helpful in PD, SD, HD, Payload, all altitude and of coarse cluster/atlitude events.
Hope this helps