Find intersecting point on line from perpendicular point

When my bullet makes contact with an enemy, I want to move it back a certain amount so it collides at the right position. I used to do this by just changing the bullet's position to the hit point position (using a simple raycast) when it made contact but now I have "thicker" bullets that use spherecasts. I want to move the bullet back instead.

I have all three orange points. I want to find out what the blue point position is.