Well, I thought I'd update this thread since I have some experience with them now.
I was able to locate and acquire a TA11 (that's the 3.5x, 2.4" eye relief, BAC, red donut reticle) about a week before I left for the
RM3GM. Until then, I was planning to use a TA01 (the 4x model, no BAC) I had borrowed from a friend for the match.
The 3.5x is quite a bit larger than the TA01, but not unwieldy on an AR.
TA11
TA01:
Here is the difference in reticles:
TA11:
TA01:
When shooting the TA01, I felt as if I was really "in" the scope. That is, the eye relief is so short than my glasses had to be
really close. Consequently, my peripheral vision was more limited and this made target transitions slower. At close range, the TA01 was difficult to use quickly.
To contrast, the TA11 has much more flexible eye relief. Since you're not so close to it, some movement during quick close shots does not disturb the sight picture as much-- or maybe just makes it easier to re-acquire. The fiber-optic lit "BAC" donut reticle is extremely fast to pick up. The BAC operation can be seen when scanning with regular 1x vision at targets; when you put the gun up, the red donut (a dot at close range) is superimposed on the background. Then when you sort of "look through" the scope, you zoom in. It's neat. And fast.
The crosshair reticle of the TA01 is much harder to pick up quickly on close targets.
I have no experience with the TA31 (a TA01 with the TA11-style BAC reticle), but I would guess it would still have the problems with it taking up so much of your field of view, and the inflexible eye relief.
I use the ARMS #19S throw-lever mount for the TA11 and it works well, but leaves the scope a little high. JP's idea of mounting the ACOG directly to the receiver has merit, but you need their new upper.
-z