Now I just need to find one.  Will an ARMS #40 BUIS work with this optic?

With the ARMS 19 or 19S it will clear, by a hair.

With the Trijicon mount, in most cases it wont.

Contact C4iGrant @ [email][email protected][/email] or [url]www.gandrtactical.com[/url].  The last I heard he had them in stock.

You may want to consider the TA31A as your M4 CQB optic.  Many have stated that the chevron is the most difficult reticle to acquire in CQB conditions because of its small signature.  With the TA31A, you still get the precise aiming point (tip of the triangle) but it also has a larger signature for faster acquistion.  The TA31A is a 4moa triangle so targets at 100 yards or less has a relatively small area that is obscure by the reticle.

TA31A on top and TA31F on the bottom:
[img]mysite.verizon.net/vze1ywph/JPGS/TA31S.jpg[/img]

Chris @ Eagle Firearms has the Ta31A for $814 on EE.
[url]http://www.ar15.com/forums/topic.html?b=7&f=23&t=166858[/url]