I'm not sure it's a timing issue but instead a hitbox one, the game has a very narrow chamber hitbox in its effort to fake it being physics based which makes chambers unworkable in practice. Enlarging the chamber hitbox, similar to how the block hitbox works, would remove some of that. The other issue is the animations being a bit awkward in how far back they start which makes the position required to chambered often counter-intuitive.My suggestion is to simply extend the window of time required to perform a chamber. I do not think that the stances are necessarily problematic and do not find getting into the correct stance to be too difficult.
Good job on the 10 chambers!