Bit syntax

[Bob Cowdery]

Hi

I'm clearly not understanding the bit syntax properly. Could someone
explain to me what I am doing wrong here. Why does the first not match
when its the right shape but the second does when its the wrong shape. 
The bound values don't make much sense to me either.

Thanks
Bob

1> <<A:24, B:48, C:408>> = <<16#effe02:24,16#00:48,16#00,(8*51):408>>.
** exception error: no match of right hand side value
                   
<<239,254,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
                      0,0,0,...>>
2> <<A:32, B:48, C:408>> = <<16#effe02:24,16#00:48,16#00,(8*51):408>>.
<<239,254,2,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
  0,0,0,...>>
3> A.
4026401280
4> B.
0
5> C.
408