In the match chamber, the bullet of the round is pushed into the rifling. You can feel this when you close the action on a round and see the marks if you extract the unfired cartridge. The theory is that this makes it more accurate and perhaps it can be seen with a machine rest and match grade ammo. Most .22s show a preference for one brand or another. My match barrel does better with the premium and good enough with the cheap stuff. Minute of bushy-tail at 50 yards makes for a fun day in the woods.