Here you go Aquashrimp:
Mig 29 uses a GSh-30-1 single barreled linear cannon. The Mig 29 originally had a max load out of 150 rounds, however this was reduced to 100 rounds.
The life of the barrel was approximately 2000 (read thousand) rounds. This wasn't because the barrel was trashed. The barrel was manufactured to a
fairly close tolerance in diameter to improve accuracy. It was replaced when it exceeded the tolerance.
Amazing what a little research can turn up eh?
RTR