I have the same opinion of the deep patent breech illustrated in Acer's post. The breech Dan promotes is not nearly as deep, so should be easier to clean, in addition to offering a receptacle for powder, in the event of a dry ball.
IMHO, there are only two types of BP shooters, those who have dry balled, and those who are about too. With that in mind, I kinda like the breech illustrated in Dan's post...not that I have been known to dry ball.
God bless
Post script;
I just remembered the first flint gun I bought, back in the early 80's. I shot that gun heavily for nearly 15 years, before the frizzen wore completely out.
I removed the breech, for some unremembered reason, to discover that the flat breech had been drilled about a half the diameter of a drill bit, roughly 3/4 of the way across the face of the plug. Though I had been shooting this gun, heavily, for several years before removing the breech, the cavity created by the half diameter of the drill did not appear to be corroded, or show obvious signs of rust or neglect.
My cleaning regimen consists of sloshing water and a little soap in the bore, swabbing with the first patch, and flushing out the breech under pressure of a tightly patched jag. The process is repeated once or twice, then the bore dried.
I suspect that flushing the breech, under as much pressure as one can generate with a tightly patched jag, has kept that cavity sufficiently clean that it has not corroded over the years.