The Brown Bess was Britain's first standardised firearm. Hence its proper name the Land pattern musket.

Before it came into service the British military used a variety of muskets using Dog locks. Which was essentially a flint lock but only capable of a single mechanical movement, i.e. there was no 'half cock' position.

I'm not an expert, but I do know that last Dog lock muskets in service with the British Army were the same 0.69 caliber as the 'land pattern muskets' coming into service. if you visit museums such as the Royal Armouries, you'll see a whole host of different styles and types of 'dog lock' muskets, varying by where they were produced and the regiment or service that procured them.