Hi monomind,
done 100mg unseparated SR harmalaHCL often in the past with good results, in 2ml standard kitchen vinegar. Is more possible? I guess but you want to keep it in, so better to restrict to the minimum effective dose to give the least internal exitation. Used to drop in 40 to 60mg fb deems in same 2ml as well, if necessary heat few sec in microwave til warm for total dissolution, then cool of to luke warm before inject. IIRC end pH somewhat 5.
Logically, first one has to be emptied to avoid/minimise the feeling of internal pressure. Even then, the presence of alkaloids can induce a cannot-hold-it-in battle. It's a false alert because it's only 2ml volume. One can win this battle until that feeling spontaneously disappears suddenly, or loose that battle and run for the pot, duh. This was typically in first sessions, but eventually this became a non issue anymore, that occasional battle feeling disappeared for good.
Used 1 ml needless syringe, diameter is only few millimeters, 3 shots to empty the end volume. Canal and syringe was beforehand "greased" very slightly with an anal pomade or alike to avoid friction.
Idk if this is the most ideal doses and practice, it just ended coincidentally this way for me.
I skipped the roa due some hassle, the disinfecting of tools (mixing recepient, syringe,..with ethanol), the pregreasing, but actually the enveloping experience of the trip can't be smoother than this, very predictable ideal rampup and if deemstered absolutely without the fear component, such a natural and at-home feeling transition.
I hope this helps, much appreciation for comments or alternatives.