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