You can chamber every attack possible in this game (even couched lance, even with fist, at least since last patch), whether they are held/feinted/cross-feinted 360° jump or anything, as long as they release an attack animation you can chamber it.
Chambering held attacks is way harder since you will know when he will release the actual attack ONLY when he does release it.
Chambering normal attacks (without feint/hold) is easier since the "chambering" before its release attack animation is a clue of when you should then use your own "chambering" move against his attack animation.
But then, the difficulty still heavily depends on "how" your mind works around chambering people, its a special skill that requires special attention or relaxation!
The main problem with chamber is mostly the word "chamber" itself, not many people understand what it means and they often confuse it with other things.
Like putting a bullet in the chamber of a gun, "chamber" = what you do before firing/attacking.
In the case of melee weapons, "chamber" = moving your weapon into "attack ready" phase, thats the first half of the animation when you click an attack (you cant hit with that animation, you can only use it to "chamber block")
"Chamber blocking" or chambering (or offensive parry) = moving your weapon into "attack ready" phase in a way where the movement of said weapon deflect (block) an incoming attack (the second part of the attack animation, which is the deadly one), using the first half of the animation in a useful way.
The time window and the body angle of chamber blocking is extremely small.
In the case of swings, you can only use opposite swings to block an incoming attack.
In the case of thrust/overhead, you can chamber a thrust with both thrust/overhead, but you can chamber a overhead only with overhead.
Would be cool if cRPG allowed chambering of any attack direction with any other attack direction, as long as the physics implied the weapons deflect it somewhere in the chamber animation.
Would be also cool if cRPG allowed projectile interaction with chamber animation, allowing for projectile deflection (would be incredibly hardcore to pull though).
TL;DR: chamber so swag, saxon l2p