There are a few references I have from 18th century American documents concerning removal of the breech by the end user to remedy a spoiled load but I can't put my finger on them.
Here is an 18th century quote about removal of the breechplug as the best but not the simplest procedure for routine cleaning every 20 shots or so. This of course is discussing the end user (or lackey in most cases) and not a gunsmith.
The barrel should be washed at least after every eighteen or twenty fires, where the best sort of powder is used; but if the gunpowder is of an inferior sort, then the barrel will require the oftener washing. The best method of washing the barrel is, by taking out the britchpin; but as this can seldom be conveniently done, take the barrel out of the stock, and put the britch-end into a pail of warm water, leaving the touch hole open; then, with an iron rod, with tow or a bit of linen rag at the end, draw up and down in the syringe manner, till it is quite clean;
Edie, George, 1772. A Treatise on English Shooting.