An opinion on a bullet code

The following code is attached to a bullet which is a rigidbody.

static var speed;
    private var coeff;
    private var dragvalue;
    private var alpha;
    private var bullarea;
    private var secden;
    private var balcoeff;
    private var masses;

function Start()
{
    speed = 868;
    coeff = 0.1;
    dragvalue = 2;
    alpha = 1.1839;
    bullarea = 1.086;
    secden = 0.16;
    balcoeff = 0.17;
    masses = 0.535;

}

function Update () 
{
    if ((speed > 1544)&&(speed<=1699))
        coeff = 0.09;
    if ((speed > 1390)&&(speed<=1544))
        coeff = 0.103;
    if ((speed > 1235)&&(speed<=1390))
        coeff = 0.109;
    if ((speed > 1081)&&(speed<=1235))
        coeff = 0.12;
    if ((speed > 926)&&(speed<=1081))
        coeff = 0.135;
    if ((speed > 772)&&(speed<=926))
        coeff = 0.15;
    if ((speed > 618)&&(speed<=772))
        coeff = 0.165;
    if ((speed > 463)&&(speed<=618))
        coeff = 0.19;
    if ((speed > 309)&&(speed<=463))
        coeff = 0.21;
    if ((speed > 154)&&(speed<=309))
        coeff = 0.07;
    if ((speed > 0)&&(speed<=154))
        coeff = 0.06;
    if (speed <= 0)
        coeff = 0;

        dragvalue = 0.5 * alpha * (speed*speed) * bullarea * (coeff*(secden/balcoeff));
        var newval = dragvalue/masses;
        speed = speed - (newval * Time.deltaTime);
        velocity = transform.TransformDirection( Vector3(10, 0, speed ) );  

}

When fired however i dont believe this is actually adjusting the velocity of the projectile. Could anyone give their opinions on this matter?

To adjust the rigidbody velocity, you need to adjust

rigidbody.velocity

instead of just

velocity

This assumes that the Rigidbody is attached to the same GameObject as the script.