Now if you want to go back to another Century, the black powder rifles was even more corrosive. Cleaning them is a MUST.
When I shoot "black powder" today, I and most shooters use an artifical substitute called by the brand name Pyrodex. But I do recall a few years back when I used the real black powder. One incident that I recall was a day that I set my pistol or a cleaning patch or something with burnt black powder on the hood of my car. When I went back to retrieve it, I noticed a stain in the paint of my car that proved difficult to remove.
I had a revolver with several moving parts that I would hang on my wall on a rugged plaque that I made. When I finished shooting this BP revolver, I would clean it thoroughly and place it back on the wall mount. One day I removed it and the thing wouldn't cock at all. I had to disassemble it to get it to work. Luckily no serious rust damage was done.
The one thing that will accelerate corrosion in Black Powder as well as WW2 firearms is MOISTURE. If you shoot in a humid place like Mississippi or the jungles of New Guinea, then you will have a problem with corrosion. You have nothing to worry about if you live in Arizona. I take personal pride that my BP guns have no rust on them, especially around the barrel where the hammer strikes the ignitor cap and produces alot of hot residue when it fires the weapon(for percussian BP guns).
Luckily with the improvement of less corrosive powders there has been an improvement in corrosion inhibitors. Some say to use WD-40. That is good for when you need a quick protection in the field or if you can't clean the gun right away. But the way I've heard it explained is that WD-40 displaces water, meaning it may just move it deeper in a crevice or bore. Personally, I try to obtain corrosion inhibitors that we use for our aircraft, such as LPS-3 ( http://www.lpslabs.com/Products/CorrosionInh/Lps3.asp ). I also use a good oil with a teflon lubricant additive.
Since this was your first time shooting, I would check to see what type of ammo you were using. As noted, any WW2 surplus ammo but may contain corrosive powder. Another thing to think about is the material of the bullet. Most military ammo was steel jacketed. Modern hunting rounds are usually copper/bronze jackets but many people re-load their ammo using Lead bullets(usually bolt-action rifles). The lead will leave micro-pieces imbedded in any pits as it slides down the barrel and also corrode the barrel. Even if you use copper jackets, it can catch in the barrell and allow moisture to collect under it. Swabbing the barrel to remove the burnt powder is not enough. That is why most modern guns should be cleaned with a lead solvent ( http://www.gunaccessories.com/Hoppes/Solve...Lubricating.asp ). I don't worry about that with my Black Powder rifles because the lead ball is held by a cloth or plastic sabot.
Hope that scares you into taking good care of your investment.
Steve