Greetings,
Situation: You paid a large no-refundable deposit to the latest/greatest training facility. It runs an outdoor range. The forecast is for miserable weather- heavy rain, etc. It’s a serious course, 800+ rounds, multiple shooting positions, hundreds of presentations. you and your gear is gonna get wet and dirty, and probably get some ‘character’ along the way:D.
Leave the safe queens at home. Whatcha taking and why? (Handgun and carry gear).
Just a fun discussion.
BOSS
I would take the same one I would take if it were sunny and 70 degrees out. The one I carry. The one that I need to know inside and out.
For me that would be a Glock in some flavor - probably a G17.
I’ve been through the exact conditions you describe with:
Custom 1911’s
Beretta 92FS
Glock 9mm
M&P 9
M&P .45
I only train with what I’m going to be carrying, generally. If I wouldn’t take weapon X to a course with the conditions you describe I would never carry it.
I’d run a “to hell and back” Sig with hogue grips for a little extra tackiness (maybe even take some light sand paper to them) in a blackhawk serpa cqc holster attached to the drop rig with a piece of grip tape on the level 2 safety release button
just my $0.02, ymmv. Enjoy the class!
I’ve been to training classes in snow, rain, mud, wind…even had one interrupted by a tornado warning. I’ve used a variety of handguns and long guns. Honestly, if I owned a firearm that wouldn’t operate in those conditions, I’d ditch it.
For me, the only thing I change due to weather is my clothing.
Sounds like Glock weather.
I’d take the gun I carry every day because if it’s going to have problems in those environments, I’d like to know it.
Haven’t the US Armed Forces answered this one pretty well?
M9, M1911, M11, Mark 23, etc.?
M_P
This isn’t a general ‘whats the best, most reliable handgun’ question.
This is more personal–from what YOU have. Many, if not most, owners have something like ‘nice’ guns–nickle plated Pythons, engraved 1911’s, pristing HiPowers, etc etc etc. Those aren’t seen to often out in foul weather.
What have YOU got, that if you were going to have to operate out in foul weather, you’d take? What do you have that you’d actually subject to nasty operating conditions–not just carry under your rain coat, but actually take out and use, alot, in inclement weather?
There are those that will hammer nails with a nice 1911. Others that wouldn’t take anything but a tupperware piece (Glock, XD, etc).
What about you?
As stated, just a fun discussion.
BOSS
any firearm, properly lubed, would be fine.
if it isn’t then it won’t be fine in perfect conditions either (IMO)
Sounds like you’ve got some valuable experience to share.
Care to relate WHAT you used? Glocks, 1911’s, Sigs, ??? How did they perform.
If you had to pick one, what would it be?
BOSS
Agreed. But not the point of the discussion.
Example: I would probably suggest that a guy who showed up with that prized, pristine nickle plated Python his grand daddy passed on to him might want to reconsider before beating the snot out of it in a high intensity training course in foul weather on a muddy, rocky outdoor range. It would be a waste of a beautiful firearm IMHO.
But I guess to each his own.
BOSS
Corrected it for you. 
In all seriousness, i dont buy guns so they can sit on shelves. Plenty of people own safe queens but they also dont bring them to training classes. They generally also dont carry those weapons either. A safe queen is a safe queen. Any pistol a smart person chooses to carry would be the pistol they would be comfortable shooting under any conditions with.
My XDm 40 would be there with me!
Either my Glock 19 or my M&P 40. Both of them have run with no problems in conditions similar to what you described. I’ve abused the shit out of them both (sometimes intentionally) and have not been able to stop either of them yet.
GLOCK 19 or my 1911.
I would train with whatever gun you carry, including your regular holster… I ran a 1911 in a class with Vickers during a hurricane last Sept and the gun didn’t even know it was raining. 
ok, no I wouldn’t bring a nice, shiny, stainless, 1911 Champion to a class.
I would bring my M&P9
Either my M&P9 or my Armory Kote’d 1911 in my daily CCW rigs.
Glock…G17, G19, or G21.
Alternatively, Ruger P89
Best, Jon