Cap-lock must means you put a percussion cap (cupped shape) on the protruding nipple, the hammer smashes it, detonating the fulminate inside causing fire to travel down the tube (indeed, nipples used to be called tubes - but - there were also tube locks - different again)to start the powder in the breech burning. Shooting a percussion gun seems as fast ignition as any modern gun. It isn't but takes a precision timer to differentiate them.

OK - here is a hooked breech for an English single shot - rifle or smooth bore.

My 14 bore has a Hawken-style breech as Track was out of English Breeches for 1 1/8" octagonal barrels when I could not wait for them to get more in - I had to have Taylor make the rifle so I could shoot an English-styled bore rifle.

The hooked breeches of a double are similar, just 2 hooks and a wider breech block.

This is a 12 bore double shotgun my bro built, using a breech he filed out himself.

Here's another, made by a gun maker friend in Alberta/

Both of these shotguns have hooked breeches.