I just re-read the original question and it would be interesting to know what one would do for dual deploy if BP was not an option. CO2 cartridges? Some other source of compressed gas?
The trouble with CO2 is that all but one of the systems I've seen require black powder to actuate, and the one system that doesn't was designed for drones and thus has a very awkward layout for a rocket, and besides has been sold out forever.
Thinking about it though, some of the CO2 systems require very little black powder, possibly little enough that it could be taken from the motor (either DMS or reload) if one were willing to dispense with backup motor ejection
(which I am more than willing to do when I have deployment electronics onboard).
The other obvious choice would be carefully confined smokeless powder, but I'd guess that's regulated the same in Massachusetts as black powder.
After that, you get into springs, etc.
@air.command has done some neat work on mechanical ejection. Due to restrictions on black powder in many countries, some of the rockets built for ESRA (Spaceport Cup) also end up using various mechanical ejection schemes.
Interesting indeed.
https://www.ramset.com/Products/Accessories/Powder-Loads
Would be pretty straightforward to figure out a striker mechanism that could be actuated with most altimeters, but it is another layer of stuff that could go wrong, independent of existing electrical controls.
The same striker mechanism could be used to puncture a CO2 cartridge too, but these nailgun cartridges would take up a lot less space. Also available in several sizes and found in many hardware stores. Mass of the chamber would be offset by not needing to carry the mass of a CO2 cartridge, and since it would only be acting as a gas generator, the chamber might not need to be very robust. Intriguing idea!
The only measurement I could find regarding how much powder the Ramsets have was 2.3g in a .27 Green cartridge. As to what the powder is, I've seen various speculation, but if it's actually black powder, that might be a solution for Mass residents to acquire powder, though they'd need to be out of state to extract it legally.
I'm thinking about some kind of solenoid activated double-action system so the rocket could be launched in a mechanically non-energized state. The energy to move the striker into the "cocked" position would be provided electrically through the altimeter at the time of deployment. There should additionally be some kind of block mechanism to ensure drop safety.
I'd be comfortable with single-action cocked on the pad, perhaps by pulling a "remove before flight" pin.
I do wonder though in these days of monster LiPos if enough heat could be generated by a high-C battery to discharge these consistently with electricity alone.
An obvious thing I don't know is how much charge is available in those loads, and how much volume they could pressurize to 15 psi or so. It might turn out they are actually small and could only be used in small rockets.
Using it behind a piston could help it scale a bit. Not infinitely of course.