I accomplished this using something like this:


public Vector2 WeaponFireLoc
{
get
{
return Location + (WeaponDir * <X Offset at neutral angle, I used 5 but have small sprites>);
}
}
public Vector2 WeaponDir
{
get
{
Vector2 v = new Vector2(-1, 0);
v = Vector2.Transform(v, Matrix.CreateRotationZ(WeaponAngle));
if (v != Vector2.Zero)
{
v.Normalize();
}
return v;
}
}


The WeaponDir gets a normalized V2 (-1 -> 1) that points in the direction the weapon is aiming.
WeaponFireLoc returns a V2 that is N pixels down that direction from Location, where N is <X Offset at neutral angle, I used 5 but have small sprites>.

Hope that helps. I suspect it's not the only solution, and perhaps not the best, but it's worked for me.