I'm not exactly an old-schooler when it comes to M&B but I've played quite a few action games like Dark Souls, Soul Calibur, and the like. I do have some experience when it comes with timed mechanics. As far as I can tell, there doesn't NECESSARILY need to be any wonky physical-contact of weapons. When at the training ground I can semi-consistently chamber block the veteran. I have even had one or two that I used in arena tournaments in the campaign. From my observation: the window is just unreasonably small for the amount of reward it gives. Maybe I'm just ridiculously lucky with my positioning, but it doesn't seem related. It seems more that there's just plain not a big enough window to perform the technique.