Is an OOBE similar to the astral projection?
I believe that both of the terms represent the same psychological phenomena.
And how does it feel like?
A rising up out of the body. Or it can be a restructuring of the perception of "the body". Propioception, or your perception of your place in space, is the last to go I've found. Due to the nature of the drugs, or doses necessary to produce this state, it's hard to really discern distinct stages. But your sensation of where you are physically in space (lying prone, sitting down, etc.) will lose to be a tangible concept.
I find the OOBE is a unique state but a poorly defined one, which I think gets muddled in literature (especially anecdotal accounts), on account that it is often confused with ego death or NDE which I feel is distinct. To me an OOBE requires retention of the ego, the sense of "I am"-ness. If you lose complete recognition of your identity, that is not strictly an OOBE.
Is it "traumatic" / scary to leave the body?
Perhaps if the nature of the experience was inherently traumatic, then yes. However, on drugs that produce the state you'll only be traumatized or scared if you didn't prepare yourself (as should be done, the same, for every trip).
And where can one float when leaving the body?
Depends. On Ketamine I've been able to change locations, swim or fly, have complete control over the content. On mushrooms, I've looked down upon my body as I rose to the ceiling before entering a fugue state from which I came to an hour or so later, lying in bed. Granted, that was on 7g of cyans.
How did you achieve that?
The Ketamine OOBE was induced by combining ROA's. I honestly feel that is the key to getting the most out of Ketamine while reducing the need to redose, as each ROA comes up at separate speeds and enhances the high. I used roughly 75mg rectal, 75mg oral and 150mg insufflated. This led to a very short traditional hole which subsided into a type of lucid hole which I was able to navigate with intact ego.
Mushrooms was 7g.
Are psychedelics involved?
Always. Unless you want to go practice decades of meditation. Quite frankly, view your psychedelic use as a precursor to learning natural ways to achieve the same state.
If you enjoy reading on-topic material, I recommend the book The Varieties of Religious Experience by William James. It will elucidate your experiences, and give you a better foundation to integrate them with reality rather than to assume they are special in nature.
Edit: Clocktower below reminded me, I've also had this on smoked DMT before.
DMT and Ketamine have given the most "experience". There is real "knowledge" in those two drugs.