I've been trying to stop rust for years. Finally found a relatively cheap solution to the problem. I apply a product called FASTEX (similar to MiliTec 1 but cheaper)
This stuff looks like oil, but isn't. The oil base is just a carrier for the active ingredient. It's billed as a "mono-molecular surface modifier" ??
It reduces friction and prevents rust. I was sceptical, but this stuff really works and keeps on working. You must heat up the gun to 50C and then just rub it on. You wipe off the excess and handle your gun as usual - it feels completely dry and normal.
I used this on a Speed Six that continually rusted. Since I appled FASTEX the gun has not rusted, despite being carried IWB, in the car, left laying around the house etc. Have also treated blued guns with equally good results.
I don't recall the supplier's details, but if you visit the Varmint Hunters web site he has an ad on there and you can order on line