Cross-Correlation between signal and the delay version

Hi everyone. I have an OFDM signal and I simulated my feedback signal with delay version of input signal. So now I want to calculate the amount of delay. I know we can do it with matlab function xcorr but I want to do it with FIR filter which the coefficients are the reverse of input signal. I calculate with both Xcorr function and with FIR filter but the FIR filter answer is not correct!!!!!!!!!! what can I do? Please help me guys. Here is my code:

T = (7e-6/64)/2;

Fs = 1/T;

ofdm_symbol = func_ofdm_generate('16qam', '8k', 1/32, 1);

x = abs(ofdm_symbol)/max(abs(ofdm_symbol)) .* exp(j*phase(ofdm_symbol));

R_input = real(x);

I_input = imag(x);

h = dfilt.delay(5); %make delay version

FB = filter(h,x);

R_FB = real(FB);

I_FB = imag(FB);

xcorr_signal=filter(conj(R_input(64:-1:1)),1,R_FB(1:1:64));

%D = finddelay(R_input,R_FB);

K=xcorr(R_input(1:64),R_FB(1:64));%calculate by matlab function

delay1 = 64-(find(K==max(K)));

delay2 = 64-(find(xcorr_signal==max(xcorr_signal)));

Best Regards,

Arash