I have left a charge in My ML for over 10 months (I got lazy) and it went off fine and was right on the money when I fired it at the target. During our Hunting Season we get Rain & Snow and I have Hunted for days in the rain and My ML still went off. I have shot it after a few days in the rain for a pice of mind, but when I did all was well. I put tape over the end of the barrel and that method has never failed me for keeping out moisture.
I know some of you will disagree with me on this one......a-lot of times are Temperatures here while Hunting are COLD! 10degrees and below. My ML goes from COLD to a WARM Truck and Home. If I dont score on a Hunt I bring My ML in for the night (without) discharging it (the 209 Primer comes off) and when needed on the next hunt it fires just fine even if it's been a week or more. I got tired of fireing it and cleaning it after every day of Hunting for no reason. This gets expensive when you Hunt every day for over 5 weeks. Plus at the end of a evening Hunt by the time I get back to my Truck it's dark and I dont want to spook the Big Buck I have been after, so I dont fire it. I think by me putting tape over the end of the barrel and being sealed up water tight this helps a-lot. I have never had a problem with moisture and a shot not going off. I do change my 209 Primer through out the days while hunting.
If your not confident in your ML and want to be sure, fire it and clean it after every hunt, then there will be no surprises. Oh and I use Lose powder and pellets with the same results.
(BP)