Unable to plot Bifurcation diagram of duffing equation

    bifurcation(dmin_, dmax_, nd_, gamma_, A_, ndrop_, nplot_, 
  psize_) := (T = 2*Pi/omega;
  g({xold_, vold_}) := {x(T), v(T)} /. 
    NDSolve({v'(t) == 
        0.847 x(t) - 0.0721 x(t)^3 - gamma*v(t) + A*Cos(omega*t), 
       x'(t) == v(t), x(0) == xold, v(0) == vold}, {x, v}, {t, 0, 
       T})((1));
  f({x_, y_}) := {omega, x};
  ListPlot(
   Flatten(Table(
     f /@ Drop(NestList(g, {1, 0}, nplot + ndrop), ndrop), {omega, 
      dmin, dmax, (dmax - dmin)/nd}), 1), 
   PlotStyle -> {PointSize(psize), Hue(0)}, 
   AxesLabel -> {"(Omega)", "x"}, AxesOrigin -> {dmin, -0.3}))


bifurcation(0.1, 0.8, 200, 0.01, 0.00172, 1200, 500, 0.006)

I am expecting chaos around somewhere near omega=0.45 but instead I am getting just straight line.Straight line bifurcation diagram for given parameters