Very late to the party, but something is rotten in Denmark here. Boosters shouldn't have any CAP or DELAY to scrape out, they should be just a nozzle and propellant. I haven't done MicroMaxx in some years, but I know all my 18mm and 24 mm boosters, when you look at them from the forward end, you see BLACK powder staring at you, as opposed to non-booster motors which have the grey cap.
I think there is more than one reason you can't (or at least should NEVER) use a standard motor with ANY delay, no matter how short, as a booster motor.
The first reason is that you don't WANT any delay with BP staging. It's different with electronics, there you may have tilt or altitude locks so sustainer won't (or is less likely to) light if it is in unsafe position (hopefully.) With BP motors, the motors don't care which way the rocket is pointed or how high it is, they will (usually) stage regardless.) Having no delay doesn't PREVENT off axis staging, but the SOONER the rocket stages, the less time it has to get OFF axis. So staging with black powder is less efficient than electronics. Fine with me, I like to SEE the staging and FIND the booster, so I am more than happy to have staging occur as long as the rocket has left the rod (I had one stage on the rod once, it was.....interesting.)
But there is another reason. Standard motors when the ejection charge goes off blow chunks, chunks of clay cap and propellant. These chunks, even if propellant, or not likely to ignite a booster since they have to get through the narrow nozzle. Despite Stine's book, it has been shown that black powder BOOSTERS ignite the sustainer by radiant heat from the hot gas coming up from the sustainer, and this is best achieved with pure black powder with no cap or anything in between.
I'm also not convinced the tape is needed even for non-gap staging, the motors are so darn close that the gas should bet there before the pressure blows the sustainer off. WITH a gap you definitely need well placed vent holes to prevent premature separation prior to ignition. I've done 13 mm non gap staging with no tape and no vents and it worked fine. Might reduce the issue of POSITIVE sustainer ignition WITHOUT separation, which as you guys have noted tends to toast the sustainer.
So I am curious, Gary, did your MicroMaxx boosters have any sort of cap?