NIce - but there's no need to use, nor any value in using, "SWIM" here. It just makes the posts harder to read.
what is a good starter dose of this this resin li[k]e material
There's no way of telling without doing some kind of test. You may have to use the approach known by some as "running up", where you start off by taking a carefully measured, small amount, and then increase the dose incrementally on successive occasions. Mescaline's slow possibly onset makes this a little trickier as well, since you may be tempted to take more before it has properly kicked in.
Add to this the fact that you're using a powdered material of unknown providence, and you'll maybe see why we recommend obtaining a live specimen of a known active clone and growing it yourself. There are risks associated with using material which you did not prepare yourself from fresh plant cuttings.
You might want to take a look at the CIELO extraction instead. This way you'd end up with a measurable amount of material with a reasonable assurance of purity. That said, there are some more cactus resin threads around here from which you'd likely glean some useful dosage information - but again, it's a bit hit-and-miss to extrapolate from someone else's experience when you're using cactus material from an unknown source [i.e., in terms of the species, variety, and growing and harvesting conditions along with post-harvest treatment: dark storage of cactus cuttings for a month or more can increase their potency by a significant amount.]
Or you could aim for a ballpark dosage estimate by calculating the likely percentage strength of an average San Pedro powder, convert that to the ratio of resin obtained from the amount of powder you used and cross your fingers. Some resin is nonetheless unexpectedly potent on account of the secondary substances contained in some varieties of cactus. This adds a further nuance of variability in potential outcomes when using a crude plant extract such as this. That is to say, even if you were to obtain the percentage mescaline content of your resin through some kind of chemical analysis, there would still be the possibility of effects diverging from the expected level of intensity or duration on account of this. See
@blig-blug's
recent experience report on cactus resin for a bit of insight on the topic.
Having a play with the
search function might lead you towards some further helpful information as well.
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