Oh goodie. A can of worms. :haha:
If you're just starting to build, grease the barrel well with a heavy gun grease. If you build at my speed it may be two years before you're ready to shoot it.
Before you shoot it, flush it out well with WD-40 (to dissolve the grease) and then acetone to remove any last WD-40. Then, wipe it with a little penetrating oil like Rem-Oil or Kroil followed by a well lubed patch containing Natural Lube or equivalent (like Stumpy's Moose Snot). Before you take it to the range, run a dry patch, and then flip the patch inside out, very lightly lube it and wipe several times to form an even THIN coating of lube.
Personally, I don't go for the "season" philosophy. I want the bore spick & span clean and then a light coating of lube just before I use it. No matter what you cook with (cast iron, aluminum or steel) you lube it BEFORE you cook. :winking: I scrub my cast iron skillets, burn off the moisture and then wipe them lightly with olive oil before I put them away. I then wipe them again before I heat them up. Nothing sticks and they cook just fine.
My sister-in-law leaves a skillet on the back of the stove and brings it forward to cook, putting it back without removing it from the stove when she's done. I guess the cats get the larger chunks of food still in it overnight. I don't eat there anymore.