per tick the movement will be:
x: cos(startangle+turnrate*elapsed_time)*bulletspeed*dt
y: sin(startangle+turnrate*elapsed_time)*bulletspeed*dt
turnrate = turnrate per time
Since dt is not constant, you can't solve the integral up front. Nonetheless you can approximate it, if you can assume your game to run at a stable fps, because then you can basically see this function as
cos(A+B*x)*C where the integral would be sin(A+B*x)*C/B
x is your time
C = the constant dt you expect (60 fps -> 1/60) multiplied by the bullet speed
A = starting angle
B = angle turned per second
the result would be the x-position in relation to the starting point of your bullet
Maybe it is possible to eliminate the dt by adjusting the turnrates dynamically along the process, so that the function will look like this:
cos(startangle+turnrate*dt*60*elapsed_time)*bulletspeed*dt
I am not sure how the turn angle expression should look for that, though, maybe a simple
every tick: set angle to angle+turnrate*dt will do the trick.
edit2: yeah I guess this will suffice and makes the end point not reliant on fps:
s000.tinyupload.com/index.php