Most folks don't know or care about zeroing their BUIS. If they did they'd discover zeroing is not possible or only narrowly possible when their rifle has a mil-spec height BUIS or BDC on the receiver and something like an A2 front sight base height for whatever front sight the shooter has acquired or selected for his gun. Typically, this sort of sight combination will shoot high when the front post's base is initally flush with the front sight base or A-frame, even if the rear sight has an elevation control which has been set to the lowest setting; and, therefore, for such a sight combination to be zeroed, the front sight post will need to be raised out of the hole 10 MOA or more, depending on sight radius. This puts the front post almost out of its hole and the post will usually be loose too.
At any rate, for those just getting into the world of AR's make sure that front and rear sights are compatible. Learn what an F marked front sight base is all about and you'll be able to think out what will work for yourself. BTW, the F marked A-frame is 40 thousandths of an inch higher than an unmarked A-frame. Don't believe anyone who tells you this is not meaningful.
At any rate, for those just getting into the world of AR's make sure that front and rear sights are compatible. Learn what an F marked front sight base is all about and you'll be able to think out what will work for yourself. BTW, the F marked A-frame is 40 thousandths of an inch higher than an unmarked A-frame. Don't believe anyone who tells you this is not meaningful.
