I've been reloading for longer than I care to think about. I didn't have a mentor nearby so I had to rely on phone calls and reading whatever I could find when I was getting started. Along the way I learned a few things the hard way, but luckily I never had any significant damage to a firearm, it was primarily confined to embarrassing myself. I'm sure most of us have made mistakes along the way and thought perhaps you'd like to share your thoughts and experience. I'll start out with a couple of my earliest sources of confusion.
My first centerfire rifle was a bolt-action .308 and so was the first bottle neck cartridge I reloaded. I had bought some PPU range brass and was trying to improve the accuracy in my rifle. I'd heard about neck sizing so I decided to give that a try. I quickly discovered that I could only neck size once or my cases would stick in the chamber and extraction required a mallet on the bolt handle. I was very confused for quite some time but I finally figured out that the problem was the neck sizing. I don't know if someone had annealed the entire case instead of the neck area only or if the brass was simply unusually soft but once I quit trying to neck size more than once my problems went away. I'm much more savvy now and pay attention to things like extraction and bolt closure but for a novice reloader that problem vexed me for quite some time. I did eventually discover the accuracy issue with this rifle. Turns out the bore diameter was .002" larger at the muzzle than at the chamber. I discovered that after learning about barrel slugging.
Not long after I noticed on a .243 I have that accuracy was poor after full length sizing. If I neck sized then accuracy was very good but as with the .308 I couldn't neck size more than once. Again, after considerable head scratching and research I discovered that the problem lie with my sizing die. I was setting the die up according to the manufacturer's instructions and using the supplied shell holder but it turns out that the die was undersized and the cases were too small for the chamber for best accuracy. I learned a lot about everything from SAAMI specifications to case measuring techniques and that knowledge has served me well in the years since but again, as a relatively new reloader it was not a simple problem to identify alone.
Anyone else care to share some of your exploits?