Quoting Glenn streeter
Im thinking of making (and i will make it this time) a single barrel shotgun but i don't know how i'd make a safety and a break barrel action ,im sure it's very simple but i would like some help none the less.

Quoting Max S.
A safety mechanism is rather easy.
All you need is something that blocks the trigger from any movement. This can be achieved for example if you put an 2 stud long crank arm onto an axle. now all you have to do is to put it in a vertical position to the trigger in the safe position. If the rod is rotated it would be on fire. You only need something that lets the safety click in place...The easiest way to do this is in my eyes two slots in the safety rod that are engaged by another rod standing vertically to it with an rounded head.

If I'd build it I'd prefer Thomas Coopers working catridges (search for it), they are perfectly made for this purpose.
A hammer mech is the easiest thing of all: hammer and trigger is all you need because for a rifle like this a disconnector is nothing else than senseless.
I myself wanted to built an over-under barrel rifle with this cartridges but I kinda lost the interest in it....

Hope I could help you ;]
~Max