From what I can understand, for the bullet movement, setting speed to 0 or disabling the bullet movement should stop the bullet from moving. I don't know if using a text box or a sprite makes a difference, but I'm using a text box.
This is what I have so far
when X = 1 -> set text box bullet speed to 40
-> set bullet angle of motion to 0 degrees
when textbox X=300 -> set bullet disabled
-> set speed=0
I've tried it with the x=300 text both as a subevent, and on the same level
when I run it, the textbox moves ok, but it doesn't stop at all.