Thought other muzzleloaders might be interested in this.
It's common for ML'ers to leave their powder charge and bullet in the gun overnight after removing the cap. I have never had any problem with this in dry air, but always been a little suspicious when humidity runs high.
I decided to check it out, so every time it has been wet I charged up a conventional sidelock with loose powder (Pyro RS) and patched ball, and an inline (#11 rather than Musket or #209) with Pyro pellets and sabot bullet, then carried them inside and out a few times for temperature changes to increase the odds of condensation.
It's taken a while to get the right weather for tests, but I did this for a single overnight and tried firing, then for two nights, and finally for three nights.
Both fired fine after one night. The next time around (2 nights) the loose Pyro fired fine, but the pellets took three tries before the #11 cap finally set off the charge. The final time (after 3 nights), the loose Pyro fired on the second cap but was a little slow to ignit, and I never got the pellets to ignite even after half a dozen caps.
I'm not going to worry about my charges overnight any more, but I guess I'll be packing the CO2 discharger on longer hunts.