Sorry, the biscuit thing is an urban legend. Never happened. No evidence, no witnesses.
http://www.snopes.com/crime/safety/biscuit.htm
Origins: In 1994 comedienne Brett Butler (of Grace Under Fire fame) was using the Biscuit Bullet story in her act, telling it as something that had befallen her sister. Butler is likely not the origin of the tale though; half a year earlier the same story (minus any mention of Brett Butler's sister) was being pointed to as a cautionary tale in a newspaper article decrying urban violence.
People in show business have been known to tell urban legends as events that happened to them. Especially in the world of comedy, personalizing a story becomes an ordinary storytelling device. (Folklorist Jan Brunvand liked to show his classes a tape of Johnny Carson's telling the resurrected rabbit story, then another from about two months later in which the late Michael Landon is seen telling the same story to Johnny. Both Landon and Carson at least start out claiming it happened to them or a close acquaintance.)
Though there are no verifiable Biscuit Bullet occurrences on record, the story has at various times been presented by the media as a true story. In May 1996 a columnist for the Orlando Sentinel ran it as a true story just dripping with fabulous details in which the daughter of a reliable source had come to the aid of the stricken lady. Within the day a number of readers had contacted him to point out this was a well known urban legend, prompting the columnist to check a little further with his source. Oops; turned it hadn't happened to the man's daughter at all but to one of her clients. (At this point, one expects the "friend of a friend" chain to continue to stretch out indefinitely as each new link contacted will correct the misinformation of it happening to her, pointing to yet another person further down the line as the one it really happened to.)
In January 1996 a writer for the Fresno Bee slipped it into an article about urban violence. Again, it had reached him as a true incident related by someone he'd been talking to about gun-related issues. In April 1998 the story showed up in the Knoxville News-Sentinel, this time told as a very detailed account of an event that had befallen a truck driver (again as the rescuer, not the victim). In April 1996 a columnist for the Denver Post ran it as a cute story he'd been hearing a lot of late. Though this fellow went to great lengths to make it clear he was relating it merely as something he'd liked enough to want to share with his readers and he didn't believe a word of it, that newspaper appearance no doubt added to the story's credibility. (It's sad but true -- even newspaper articles debunking urban legends are later remembered as news stories in which the incident was reported as 100% true.)
This legend popped up again on the Internet in early 1999 as a true "dumb blonde" story, attributed to the Associate Press.
Underlying this humorous story runs the fear of modern crime's engulfing the innocent, resulting in the undeserving's becoming just another drive-by or random shooting statistic. That the loud bang of a canister of biscuit dough exploding in the heat would be mistaken for gunfire says a lot about our feelings of vulnerability.
The "food substance on the head mistaken for brains" motif is not new to this story. In Mark Twain's Huckleberry Finn, Aunt Sally says about Huck, as the purloined butter hidden under his hat begins to drip down: "He's got the brain fever as shore as you're born, and they're oozing out." In more traditional folklore, a fox puts milk and butter on his head and convinces a bear that he has had his brains knocked out. In a Russian version the fox puts pancake dough on his head and says it is brains. While these stories do not seem like the origins of the biscuit bullet tale, they certainly establish that the basic idea existed in folklore long ago.
