Fireworks.org – The World’s Fireworks Community › Forums › Pyro Technology › Any tips on getting a cleaner break on 4 inch shells? › Reply To: Any tips on getting a cleaner break on 4 inch shells?
Check your pasting consistency first. Uneven paste layers can cause weak spots that blow out before the rest of the shell. Also make sure your spiking is even. I had the same problem until I started being more careful about symmetrical spiking.