300 mg is a very strong dose if the mescaline is pure mescaline. More than that can scare the crap out of some people. I would not recommend more than 300 mg to anyone who’s not familiar with mescaline.
But the 300 mg dosage is for pure mescaline. It's very likely that your mescaline is very impure. Some extractions of mescaline can be more than 60% impurities and produce a very foggy stoning experience. Pure mescaline is like LSD, it’s a clear headed, non-stoning experience. The impurities present in San Pedro, Torch, Achuma, and Peyote, are responsible for the stoning effects, and in many cases responsible for the weak experiences had. The sedatives in these cacti have effects similar to harmaline, and while they seem to be MAOIs that greatly potentiate tryptamines, they do not seem to potentiate the effects of mescaline at all, but instead they take away from the mescaline experience.
If you want to experience 300 mg of mescaline and be sure of the dosage, you’ll need pure mescaline.
If you have mescaline acetate, you can wash it with cold MEK to get nearly pure mescaline. If you have mescaline HCl, you can wash it with acetone and then IPA to get highly pure mescaline.
There’s a thread devoted to washing mescaline on the Nexus. I recommend taking a look at it. Until you have pure mescaline, you really have no idea what it can do. Cactus is not a mescaline experience. It’s an experience of many alkaloids, of which mescaline is but one. The sedatives present are pretty strong and really mess up the mescaline experience.
While cactus is almost nothing like LSD, pure mescaline is very much like LSD.
The only part of a cactus trip that is somewhat like mescaline is the tail end of the trip. Mescaline is one of the longest lasting alkaloids in the cactus. But even then, pure mescaline is better, especially at higher doses.
SWIM found, as far as sedatives go, that Kava and mescaline are quite nice together. Also a small amount of Datura inoxia (5-10 seeds) is a good sedative for mescaline. Both take the speediness away without bringing the trip down. But the sedatives present in the cactus are not good in combination with mescaline. They add a foggy stoning effect that brings the trip down quite a bit. This is one of those cases where the natural mix of alkaloids is definitely not preferred. There are much better mixes out there.