I have a few potted San Pedro's, and would to propagate more
You just cut it and stick it in soil to root?
Discussion
So you gotta let it dry first after you make a cut, for about a week or so. Once it’s calloused over you can repot in a gallon pot to root. I do a mixture or cactus soil with some tropical soil for moisture. I would love to see some photos of your Pedro’s!
I think they're Pachanoi. Thanks so much for all the info! 
Does keeping it in the sun help with the callousing or will that dry it out too much?
Those are awesome Pachanoi!!. I would bring them inside after the cut you can keep it in a box for it to dry and callous. I don’t leave it outside because it can get scorched bad after cutting. How tall are they?
Good to know. They're probably 16-20" tall. How far down from the top do you think I should cut?
Xerics are clearly not my forte lol
I love these questions. I was in that same boat and I just asked tons of questions too. So i typically go for 10 inch cuts. Minimum is 6 inch and maximum is like 12 inch. Of course everyone has different opinions on it. That is just my preference and it hasn’t failed me yet.
applying sulfur powder to a fresh cut on a cactus can help it dry out and callus faster while also preventing infections from bacteria or fungi. It’s especially useful in humid environments where rot is a concern. If you do end up doing it this can help. Any other questions I’d be happy to answer.