There is a lot more jelly than it looks like here as all of it is double and the entire border is filled. The left cannon is surrounded by locked pieces, the right cannon is surrounded by 2 hit blocks. They basically have the same effect. Try to make vertical striped candies to shoot down the sides of either cannon to try to get one of them to shoot off early. Once one has fired, then head over to the other and clear it out.
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Patricia Frederick’s Tips on Candy Crush Level 381
Clear the cannons separately using vertically striped candy matches or striped/wrapped combos. Every time you clear a cannon, the hammer hits and a layer is removed from the entire board—a layer of candies, jellies, chocolate, blocks… So clearing them separately removes 2 layers of jellies (and there are jellies underneath the cannons as well.)