about convolution code

Hi,all
    i build 3 simulink model to watch the benifit of convolution code. 
model 1:
bernoulli binary------16QAM modulation--------awgn channel---------16QAM
demodulation---------Rx binary

model 2: 
bernoulli binary------CC coding puncture 4/6------16QAM mod--------awgn
channel-------16QAM demod---------CC decoding de-puncture 4/6-------Rx
binary

model 3:
bermoulli binary------CC coding,no puncture-----16QAM mod---------awgn
channel------16QAM demod--------CC decoding-------Rx binary

The same SNR is set for awgn channel and the BER of these 3 models are
compared.  
BER2>BER1>BER3

the question is why BER of model-2 is high than BER of model-1. 
anyone interested in my model please leave your e-mail address. i will
send you the simulink model.

thank you!