In the end I decided I'd risk it with just an mg scale, not the wisest of methods, but what I did was weigh up 1mg, and given that my scale can be say 0.5-1mg off in either direction, occasionally 2mg, I just assumed I had 3mg, divided the dose up a further 3 times, and smoked one of those little piles (the one that looked like it might be slightly smaller than the other two). In retrospect, I assume my pile DID underweigh and was 2-3mg as even 1/3 of the initial amount left me very high.
I wouldn't advise that method to anyone though, as there's no way to tell the density of a powder by eye so even after dividing the tiny amount it could have been more than expected (in fact it was, but in my case, I expected very little, and got a nice strong high - in someone else's case, you could expect a nice high and end up way too high.)
Overall AM-2201 felt really nice, unlike JWH-073 and JWH-081 (the only two I've tried before) I couldn't pin it as either sativa or indica-like in effects.
JWH-073 definitely felt like a strongly sativa dominant hybrid, quite paranoid with little in the way of couchlock or munchies. JWH-081 felt like a pure indica, couchlock, munchies, painkilling effects but no real introspection (and thankfully no anxiety) unless I pushed the dose insanely high. AM-2201 feels like a balanced hybrid, lots of introspection, a little paranoia/anxiety but not too much, very "in" my thoughts and head, but an extremely pleasant body high with nice numbing/painkilling qualities, some munchies but not much - probably due to the fact I ate right before smoking though.
One thing worth mentioning, is I've heard people say this one hits you instantly, but I'm not so sure about that. I vaped the dose off foil, and I thought either it wasn't enough or I must have burnt it, because I got a bit of foil taste, and didn't feel a thing. 5 minutes later I was about to put a second pile on the foil to vape, and the high suddenly hit me too hard for me to even move the pile. Glad I hadn't been quicker to smoke it, and goes to show that it's always good to wait say 10 minutes before smoking more with this if you're not where you want to be
