The Firing chamber was the blaster component where the plasma energy was activated and intensified in the microseconds before the weapon was fired.
Larger firing chambers allowed for wider energy beams that caused greater damage, so they were highly sought after in the customization of blaster weaponry. For example, the Mandalorians produced large chambers that could triple the damage dealt by even the smallest weapons, turning even the humblest of blasters into deadly weapons capable of blasting huge chunks out of anything it hit.