The object of the exercise was not to have the round 'burst' in the gun tube. The object of the exercise was to have the contents of the canister be effective as it left the muzzle. In effect, the round performed at 'muzzle action' being able to spread out as it left the gun tube. The round rupturing in the gun tube was the result of the effect of the charge on the tin canister. And the French canister round did precisely that as stated in DeScheel regarding the 1765 tests of the new canister round. The reference is easily obtained and I would highly recommned it to you as with the rest of the primary source material referenced in the canister threads. It is a very simple concept and one that is repeated in every primary source on artillery that I have seen that addresses ammunition and its effects.