Dude you can gap stage a Estes black powder motor like an E12-0 booster tumble recovery directly to a E-12-6 on sustainer. The ejection charge of -0 ignies the upper stage Estes motor. Look up Estes extreme 12 etc. And best part is no electronics needed there.
I’ve worked with six multistage hpr rockets using 29 and 38mm APCP H and I class motors some won national comps for multistage flights at university levels. For those kinds of builds nothing matches the ease of programming and ground testing of raven units. You’ll want to try the velocity and time check functions on it to limit the angle the rocket sustainer igniter can ignite at. There’s even advice on supersonic staging in their manuals which is invaluable.
Then you can program the parachute deploy settings on a Raven so that chute deploys with separate bp charge and electronic igniter even if sustainer motor fails to ignite and fails to ignite motor delay. Much safer than a straight up timer and I’ll credit one to saving lives.
Let’s say you only had a timer and it ignites the igniter of sustainer stage but the motor propellant does not have ignition success. Your motor deploy ejection charge of the sustainer will fail. It will come crashing in ballistic without a separate electronic altimeter that fires pyro charges for recovery of sustainer without needing motor deploy. (The raven unit has additional channels to fire more igniters to deploy a chute after the motor either lights or doesn’t light.)
The other really horrific failure method of timer only is if sustainer stage tilts in flight let’s say it weather cocks unexpected on boost after first stage separation. The timer reaches said time and dumbly fires the sustainer stage motor igniter. And it doesn’t care what orientation the rocket is at. The weather channel has a horrific accident where a multistage Hpr timer only flight ignited badly which I used to enforce to new students why we should just use a raven or other altimeter based system with some kind of tilt check. I’ll try to link it if I find it again.
They don’t even force you to use a tilt check system but I find it superior safety wise to set it up especially for apcp motors extremely especially if high power motors. If this is first multistage with bp only motors I suggest you try gap staging to other bp motor instead as it’s much simpler. If your wanting to light APCP motors get a Raven, Marsa, or Telemetrum unit that affords you some additional tilt safety.
I’ve also found most HPR sites dislike anything timer stages only and for good reason.