Ok, first off, don't use corcidin. Make sure whatever you use, the only active ingredient is dextromethorphan hBr. Corcidin has some other nasty stuff that can really fuck you up, like kill you, easily.

Secondly, I don't know why 700mg only gave you a slight buzz, that should be enough for a third plateau trip or at least a very strong second plateau. Try taking 1 1/2 bottles of Robitussin cough gels, which is 450mg. Again, make sure you are on an empty stomach and drink it with some orange juice to help with any nausea.

To ShWeave, you'll be tripping pretty hard about an hour after ingestion for about 6-8 hours, depending on which product you use. For your first time, I would recommend doing it alone because you'll probably have a pounding headache about 2 hours after ingestion that you'll want to be alone for. It would be good practice to tell some close friends what you're doing, so in case things go south, you'll be able to get help.

I've never done DXM with someone, but I imagine it would be fun.