I also find the chamber very effective against fast shielders. If you are doing a STR build and have 12 or less agi, chances are that 1h guys have more agi than you and can run right up on you turtling and then start spamming side sword/pick etc. These guys can be difficult to attack because they can swing much faster than you with their 100+ speed rated weapons. Since their weapons are so fast it might seem counter intuitive to try to chamber them but it will be very difficult to get an attack off if they can let their shield down and strike you faster than you can get a single swing off. If you watch for the direction of their backswing and instantly swing in the same direction, your slower swing should meet theirs in the middle leaving them with their guard down. If you are fighting someone without a shield that swings around the same speed you do, you generally have to wait for their swing to start or you will be too early to strike their weapon with yours.
The only way for chambering to be really useful is to practice it enough that it is a natural and intuitive reaction in combat. The way to achieve this is to think of swinging your weapon into theirs. The hit detection of the weapons are pretty good and if you are accustomed to the swing speed of your weapon well enough that blocking/attacking/fainting/chambering are all fluid reactions to the enemies around you, you have mastered 2h. A good player can often still block you after you chamber them, but this shouldnt deter you from utilizing this technique. It takes slightly more practice than normal blocking, but think of it mostly as a block and less as an attack. The benefit of it is that you are already chambered for your attack and will ALWAYS be able to outswing the other player at that point. Their only option is to block or to chamber you in return. You, in turn, always need to be ready to cancel your chamber and block a different direction if they faint you or chamber your attack.