You could try playing around with the 'set time scale' event in 'system', set it to something like 25% speed and then wait for 1 second (which will be 4 seconds in real time) and then set it back to 100% speed.
I tried to create your solution but now bullet is not even moving on click on button. Attaching capx of the file.
https://touch.affle.com/ads/bullet/bullet.capx
can u let me know why bullet is not moving on ok button click