Quoted:
I just bought a TA01 so I could use it on my fixed handle AR and my flattop AR. Am I going to have problems on my flattop since the BDC is set up for carry handle use? I do know I will have to rezero every time I swith from one to the other.
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Yes - to mount the TA01 on your flat top rifle you'll end up putting mount like the ARMS #19 (picture is of the 19ACOG as ARMS is missing the plain #19 picture)
[img]http://www.armsmounts.com/images/19ACOG.JPG[/img]
[img]http://www.trijicon-inc.com/parts/TA01.jpg[/img]
For "tactical" use you'll not notice the shift in zero using good quality mounts on the lines of the ARMS but each rifle will have it's own zero location. Recording the difference between the two in clicks you ought to be able to get close enough for government work.
I'd just put the sight on the carry handle rifle and look for something else for the flat-top like the Aimpoint Comp "red-dot-'o-death".