I have a Bushmaster AR15 with a fix front site post, and I was wondering what would be the best optic to have, without the front site post getting in the way.  Any suggestions? Mahalos in advance!

with magnified optics the front site should not be visible..maybe a small blur
I have an ACOG on mine and hardly notice it

I have a Bushmaster AR15 with a fix front site post, and I was wondering what would be the best optic to have, without the front site post getting in the way.  Any suggestions? Mahalos in advance!

The best optic to have is the one that works for you and your planned application...it's probably best to decide that first and go from there.

with magnified optics the front site should not be visible..maybe a small blur
I have an ACOG on mine and hardly notice it

^This is correct.

If using magnified optics and the blur bothers you, get a riser or high mount/rings.

I normally mount customers optics 1/8" above the centerline of the front post. Less of a blur.

I know you are not asking about an ak, but if you scroll down on the link you can see photos of an optic and how the front sight may appear in the picture.
Have a happy Aloha Sunday!

http://kaneohegs.com/inventory_rifles.htm#optimizingAKrifles

I want to set it up for CQC and maybe adding back up iron sites.

Aimpoint micro w/LaRue mount.

I have a Bushmaster AR15 with a fix front site post, and I was wondering what would be the best optic to have, without the front site post getting in the way.  Any suggestions? Mahalos in advance!

What's your budget range?  If there's no price cap I would second the aimpoint micro.  There's also the aimpoint PRO that could be had in the $400 range w/ mount.  That's what I run and fits my needs.  Definitely recommend iron sights.

What's your budget range?  If there's no price cap I would second the aimpoint micro.  There's also the aimpoint PRO that could be had in the $400 range w/ mount.  That's what I run and fits my needs.  Definitely recommend iron sights.

Do you know any shops that carry it locally?

I personally didn't buy locally, bought online during a sale.  I've seen high end optics at OGC but can't remember off hand what they had in stock... Sorry can't help you there.

Do you know any shops that carry it locally?

OGC has a great selection of scopes.  X-Ring is another store which will find you something within your budget.

I got an Aimpoint Pro for $375 shipped
They talk about deals here: http://www.ar15.com/forums/t_3_18/537184_LOOKING_FOR_OPTICS_DEALS__Post_read_here___READ_OP_BEFORE_POSTING_.html&page=8

I want to set it up for CQC and maybe adding back up iron sites.

If you have a fixed front sight post (FSP) and are trying to set up the gun for close quarters, I would recommend a red dot with lower 1/3 cowitness with your irons.  If you have the FSP, you would only need a rear BUIS.  I have two guns with fixed front sights (one FSP and one with a DD A1.5 on a free float rail) and both have an Aimpoint lower 1/3 cowitness with the irons with Larue QS mounts. 

Back up iron sights are a must.  While Aimpoints are known for long battery lives, in the 5-8 year range even if left on continuously, they can and will fail.  I've seen them go down. 

I personally have a T-1 and a Comp M4s, but the Aimpoint PRO reported to be an excellent value.  Last time I was at OGC, they had them in stock, but that was a while ago.  There are usually sales online where the optic runs in the $350-$450 range depending on what mount you get with it. 

If you have a fixed front sight post (FSP) and are trying to set up the gun for close quarters, I would recommend a red dot with lower 1/3 cowitness with your irons.  If you have the FSP, you would only need a rear BUIS.  I have two guns with fixed front sights (one FSP and one with a DD A1.5 on a free float rail) and both have an Aimpoint lower 1/3 cowitness with the irons with Larue QS mounts. 

Back up iron sights are a must.  While Aimpoints are known for long battery lives, in the 5-8 year range even if left on continuously, they can and will fail.  I've seen them go down. 
 

Agreed. 

Also for the OP, while rails and gas blocks have vastly improved in their durability and the ability to better maintain a zero, however in a true hard use or critical use rifle I still prefer a fixed front sight base by a slight margin rail and gas block dependent.  As mentioned a lower 1/3 cowitness set up allows for a better heads up orientation and allows a better view with the sights.  With the proper amount of time behind the rifle you will not even notice that they are there.  Also I prefer a quality fixed rear sight when I am using a red dot and only go with folders to clear certain optics.  If I do go with a low pro gas block set up my first choice is a shaved front sight base or a quality pinned low pro block.