why newbies, instead of learning the basic concept of functions and logic, do want to code more if they dont know how to think. but im afraid this is a IQ gap or something , because that answer is basic logic i think.
but well.
you measure the point where the bullet is emitted.
and while(no impact event)..

wait 1, and calculate the initial bullet position, to the current position.
also, add movement, with c_scan or anything depends on what you want to do.

After the impact the while loop is break, so you know its zero, then explode or remove.. or you use the calculation speed formula.. s="delta"positions/"delta" time. and if zero, trigger removal. with ent_remove i think.

good luck.