One time after hunting, I wasn't able to clean my ML for 2 days after 1 shot had been fired using 777 powder. I cleaned it thoroughly afterwards, and there was no damage to the barrel - it's still shiny like new. However, I wouldn't make a habit of it- better safe than sorry.

I use a solution of 50% Windex and 50% rubbing alcohol - works like a charm to clean the barrel. I don't ever use oil-based products to clean the barrel - only to clean/lubricate the breech plug, bolt, trigger, etc.