I have an IOR 3X25 optic.  I like it mounted on the very back of my flat top.  Would there be any real reason to not put a BUIS in front instead of behind it so I can leave my IOR where I like it?

The Canadians put their fixed BUIS on in front of the Elcan scopes, so I don't see why not. But if you put it on there, you'll have to sight it in there, and understand you have shortened your sight radius.

Yea I know.  It's on a mid length RRA though so it wouldn't be that much shorter than an M4 sight radius.

Thanks for the pic.  I just got a midlength with LMT fixed buis, and have been wondering how to make it "play nice" with an optic in the future.  Is your ACOG mounted all the way to the rear?  It looks like real estate is a little tight in front, and the LMT base looks bigger than the LaRue.

Does the sight cause much obstruction or ghosting in the optic's image, or is it easy to ignore like the FSB?

With changing the location of the rear sight, how far off would the A2-style elevation wheel be?  Minimal or moderate/severe (in which case I'd do the IBZ and leave it alone)?  It'd be nice to have that functionality, but these are backups.  

The ACOG is sitting one notch farther back than it would sit with a folding rear BUIS.  You couldn't get an LMT on there.  There's not enough room on the rail.  You could put the ACOG farther back, if you're not a nose-to-charging handle kind of person.  You can't see the sight at all in the optic.  All I can see is a ghosted FSB.  It really works very well and the sight could always be slid to the rear if the optic goes tits up.

Thx for the info; lots of newb questions here.  I was worried the sight would be way off if I slid it back or even stored it somewhere on the handguard rails.  There's some extra real estate uncovered by the ladders under the barrel at the front, and the sight fits there.  I know the QD mounts on other sights/scopes are designed for repeatable zero, but don't know much about thumbscrew mounting.

The LMT won't fit at all with the ACOG, or just won't fit with it mounted a little forward?

Tx again, and Happy New Year.

It won't fit where I have the ACOG mounted.  I shoot nose-to-charging handle so mounting the ACOG any further back wasn't an option for me.