[Shortdrift]

My ML is one of the first manufactured and has a completely exposed breech/nipple/hammer section. Like crappiedude I store it muzzle down.
I have never had a misfire while hunting or at the range and all I ever used were standard caps. I keep the caps stored in an airtight container but I also go to great lengths when preparing my ML for shooting.
My ML does not have a breech plug so I have to really get the breech and bore as dry as possible. I start running several patches soaked with bore cleaner to cut the storage oil. I follow this with a couple ounces of rubbing alcohol poured into the barrel with the cap nipple plugged. I'll rock the barrel for a minuted or two then dump it and again dry patch. I let the barrel sit muzzle down for a while, dry patch again then follow this up with a flush of high grade automotive laquer thinner and drain through the nipple. The thinner will evaporate very quickly and leave a dry breech and bore. I load the gun ( I shoot patched round balls and Pyrodex) and don't reload if unfired for several days. If i'm hunting in the rain I cover the muzzle with a latex finger guard and also protect the hammer/breech area with some saran and a rubber band.
Lots of precautions but the gun always fires.