This has been an interesting tread. I don't fly HPR, so I avoid responding in the HPR topic group. Nevertheless,...
There is an old anecdotal story about Alan Pope, a highly regarded aerospace engineer, who had or developed some experience igniting composite propellant motors. At some point the army or AF released a bunch of aging motors to other responsible organizations. The new users had some difficulty igniting them. Alan reasoned that the propellant needed both temperature and pressure to combust, so he started gluing a common jack ball from a kids toy set into the nozzle throat with rubber cement. This worked well and news spread. Some manager "down south" thought he had grasped the concept and he had a conformal aluminum plug machined to fit the nozzle. This was glued in place, and the motor CATOed on attempted ignition. The manager then decided enough was enough and he insisted on flying Alan Pope and an assistant down for a hands on demonstration. Alan explained over the phone how simple his technique was and that a trip was not necessary, but the manger insisted. So on their drive to the airport they stop at a Ben Franklin's store and bought some jack balls and rubber cement. And everything goes well from then on.
I have flown many Enerjet F67 and E24 motors, ignited electrically with the supplied long Sure-shot like igniter wick. I never had a problem and it was common practice to tape over the nozzle, or even form a cone of masking tape to fit the nozzle, I usually just tamped in a small ball of wadding like on an Estes motor. This caused no problems and seemed to avoid slow starts. The only problem was that it took a second or two for the wick to burn and start the motor. Around this time there were electric matches available that worked on lower current and I even used them to ignite F100 BP motors. I never tried them on an Enerjet motor. I was concerned that a piece of the igniter might jam in the throat and cause a Cato. At some point the NAR decided that the ignition delay was a safety concern and they had the NFPA codes changed to require more instant igniters.
Over the years, a number of composite motor manufacturers have come and gone, with their own igniters. I've always favored following the manufacturers instructions and using the supplied igniter. I have had some difficulty installing provided igniters in small AT motors with offset cores or slots, but they always worked. I confess that I was a little bemused when AT started to insist on cutting a vent in the nozzle cap, and even using a vent tube on the new Quest motors, but again, I prefer following the manufacturers instructions. I get concerned about adding dowels and bits that could potentially plug the nozzle, but it is hard to argue against them. I'm even concerned that long igniter leads could jam in the nozzle throat. I'd like to see head end igniters used, but that is not practical for the SU motors that I prefer. I understand that some motors are now supplied without igniters. I understand that many old reloadable grains should have their ignition surfaces sanded before use. And yes, I understand that we need to temper following the manufactures instructions with using techniques that have been proven to work. Again, I'm not an experienced HPR flyer, so take all of this with a grain of salt.
