When I had this issue I discovered that when the oven pre-heat cycle is on the top broiler turns on, which gets things too hot. Now I just wait until the broiler burner goes off then stick the bullets (just dumped on a wire tray) in and let it cook for 15-16 minutes. This is with a $8.70 thrift-store toaster oven that has worked fine for years now.
Loren