Back in the 70s I had a similar experience - had a set of Hm300s on my K2, and was proddy racing, so needed to put some baffles in to pass scrutineering - had a set of Hm341 end cones, so with a bit of effort late the night before the races banged them into the ends of the pipes (they were a very tight fit), and of course hadn't lined up the holes to put the bolt in. So got through scrutineering, out on to the track and first race - mate following me through the esses oh his CB, hot on my tail, when I noticed, as I twisted the throttle to the stop as I exited the last turn, that the exhaust note suddenly changed.
He passed me a bit later and shook his fist at me - WTF - ended the race, and back to the pits. He came up to me wetting himself laughing - one of the baffles had shot out at great speed and just missed his helmet.....
hahaha, we went for a walk after the racing and found it in the grass trackside.
Could have been a different story if it had hit him!