Hi kristian,
Personally, I feel that DMT is a very reliable vehicle for OBE's. I used to have OBE's regularly on mid-to breakthrough doses of DMT. In particular, when I vaped it all under 60 seconds but also held good long times, OBE was almost guaranteed for me.
A lot has happened since those early days. It is very difficult for me to take a breakthrough dose these days. When I do it is a lower one (e.g. 35-40 mgs in the GVG). I think the hundreds of trips, close to a hundred breakthroughs and all that has happened have come together such that when I currently consume breakthrough doses, I am still aware of my body. Sometimes I feel like I'm floating right above it.
Also worth mentioning in my limited experience was that once I had a really fun astral projection trip with pharmahuasca (approx. 3.5 grams syrian rue and 70 mgs fb DMT) - was up out of my body and then floating above the apartment, then trying to move to where my husband was - 80 miles away at the time. I wanted to poke him or something then call when I baselined .. . . Anyway, I made it over a set of hills but then got lost in all the tryptamine details. Needless to say, it was nice having the extended timeframe of the pharmahuasca trip within which to explore this.
Here's my thoughts on why it is so difficult to achieve: We don't think about this very much but a lot of our ego and self image is intimately tied in with our bodies and our perceptions of our bodies. Letting that go, letting the physical body go, is the ultimate act of complete and utter surrender. It oozes with death themes. It can be scary and difficult.
But, it is soooo worth pursuing in my humble opinion. If you can surrender and just let go or somehow get blown out of body so fast and hard that you have no choice, frequently (again, just using my own personal experience as a guide here) the payoff is wonderfully spiritual and mystical.