Boxlocks: Pull trigger, go boom. Just about every country that can make a decision on what colors it's flag should be has a population with the skill to produce a sound boxlock-sidelocks, not so much. A sidelock is pretty much a hammer gun with the hammers moved inside, and when things go wrong, they require talent, expensive talent, usually, to make it right.
Boxlocks are far better at frustrating Murphy's law. Period.

Best,
Ted