While I have no problem with AC40, per se, I did encounter an issue with one recently.
I pulled my Heavy Metal out of mothballs to play around with possible builds for it. It has FULL ARMOR, 100% maxed, including 60pts on each side torso, front. I was in a position in River City where only 2 enemy mechs could possibly have had a direct line of fire on me, and one was trying to get away (back turned). The other was a K2 that I had seen peeking, and shifted my aim to engage when he popped out. When he did, he took one shot and removed all of the armor from my RT (at least 50 points at the time) AND sent the IS to deep orange.
I know for a fact there were no other shooters, my paint had barely been scratched, and he didn't have the firepower to hit me that hard. It's possible there is an issue. I couldn't say if it's an AC20 issue, limited to AC40, a broader AC issue or possibly an issue with multiple ballistics. I can only attest to what I saw, and the numbers don't add up.
It's also possible it was just a freak glitch, but figured I'd throw it out there.
Edited by OneEyed Jack, 25 October 2013 - 02:13 AM.