Everyone agrees add powder, and the consensus is you probably want to have around 3 grams total, so how do you do that?
I fly Aerotech DMS motors and CTI motors. The DMS motors come with the pre-measured ejection charge packaged in a small plastic vial with volume markings on the side. (I assume Aerotech reloads are the same.) I thought they usually come with 1.4 grams, but someone upthread just said 1.7, which may well be true. I don’t really remember. You can use those vials to measure your supplemental charges. I’ve saved up a bunch of them and keep a few in my range boxes.
For DMS, the full 3 grams won’t fit in the charge well and allow you to use the usual red cap to seal the charge well. What I do is put a wrap of masking tape around the top of the charge well to make a little tape cup to extend the rim of the charge another half inch or so. After you drill your delay, dump the pre-measured charge into the charge well. Then pour some ffffg black powder into the vial until it reaches the volume mark for your supplemental charge. I fill it up to the 1.5 mark. Then pour that into the tape cup/well on top of the BP you already added for the standard charge. Then fold or twist the tape shut to seal up the whole 3-gram charge. You don’t want any extra space in there, so if the BP doesn’t come all the way up to the rim of the charge well, pack a little dog barf or wadding in on top before you seal up the tape so that everything is nice and tight. Add some extra tape if needed to keep it all secure.
For CTI, it‘s the same basic idea, except the factory ejection charge is already sealed. Just leave it like that and assemble the motor in the case as usual. Measure out your 1.5 grams supplemental charge. I use an old spare DMS vial just like I do for DMS motors. You can make a tape cup for the extra charge right on the end of the case, which is what I’ve mostly done. You have to be careful because wrapping the tape around the end of the motor case can add enough diameter to the case it can be more difficult to slide into the motor tube. And if you have to pull the motor out before flight for any reason, be sure the tape cup doesn’t peel away from the case and dump the supplemental charge. Another option is to pour the supplemental charge into a small square of wadding, fold that up, and then tape that to the end of the case right above the factory charge. The factory charge will blow right through the wadding and light the supplemental charge. I’ve been using that method the last few times.
I’m sure the method for Aerotech reloads is pretty similar.
