I have a 24" Colt HB Elite Barrel.I got a front sight post pre ban .750.It slips onto the barrel easily.My issue is the holes for the pins do not come close to ligning up to tap them in.If I take the front guard cap off it still can not move back enough to align the holes.Any suggestions? Does it need a post ban post?

The holes are not placed the same distance on the sight posts of the preban and postban barrels.  I tried this and found out exactly the same thing.  You will also find that between different preban barrels, the holes will not always line up between different bayo lugged sight towers.

Thanks raptor22,
I'll save it for an 2004 m4sunset and look for a post ban version.

Man, that really sucks balls!  I found that out too.  I sold off sight towers cause at first I thought I had some nice spare parts for new rifle builds only to find out it was hard to get standard barrels without sight towers and even if I could, the sight tower I would try to install may likely not align.  If you stay with preban to preban or post ban to post ban, and use the same manufacturer for the sight tower as the barrel, you have a much better chance the holes will line up.  Since the manufacturers usually drill the holes with the sight mounted for perfect alignment, your new sight tower may fit but not be in alignment. [banghead]