Yes I have had experiences that I am aware 100% were astral projection. The first time it happened to me I thought I was dying of a stroke...until a very good friend told me what it was and stopped me being scared out of my wits.
After this was repeated at least 50-100 times after that I know what it is -just the way I know my hand is joined onto my arm.
How to prove it to somebody else who has never had such an experience, and isn't there to witness the actual event?
Impossible. How do you prove the sky is blue to someone who is blind?