For a variety of reasons, keep a journal of your shooting activity.
If you own only one rifle, then your record-keeping tasks are pretty easy. If, as for many hunters, a season of hunting doesn't consume a box of ammo, then keeping a running total of shots fired is pointless. In your lifetime you aren't going to shoot enough to need to worry about how much accuracy is left in your rifle. After all, 50 seasons of 20 rounds each is 1,000 rounds.
I know one old hunter who kept track of how much he had shot and how the ammo fared by keeping the torn-off flaps of his ammo boxes in a cigar box. On each he would scribble the results of the hunting that season. A summary of his results, year by year, would elicit a routine "neck shot at 30 yards in the swamp, neck shot at 25 yards."
The rest of us have more to keep track of. A simple record-keeping system could just be a stack of file cards held with a rubber band and a running total of the ammo fired through each rifle or a loose-leaf binder with a page or section for each rifle.
The most elaborate I've seen was a spreadsheet where the owner tracked each rifle, noting the number of shots fired, accuracy levels, hunting results, dates, weather conditions, which reloads or factory ammo were used, chronograph results and (I kid you not) his biorhythms for the date. I swear he spent more time fussing over the spreadsheet than he did shooting, but he could produce very impressive groups if you asked.
I tailor my record-keeping to the rifle used. Some get just a rough note of how many rounds have been fired. My rifle for law enforcement patrol rifle classes only has a rough count of the number of rounds it has sent downrange. I loan it to students when their rifles go down and clean it when it needs it. It gets hard treatment, and I only need a rough idea of rounds through it so I know when to test the barrel for accuracy before replacing it. I just jot down some appropriate notes in a binder when I get back from the range or a class.
Other rifles get a more thorough set of notes. When I first acquired my M1A, I had bought it with the intention of building it into a competition rifle. I had planned to change everything, especially when the previous owner told me as part of the bargaining that the "bore was shot out." I believed him at first and ran through the rest of the two cases of surplus .308 that came with the rifle in practice and match sessions that lasted that summer.
When I finally got around to cleaning it, I noticed that none of the gunk coming out of the bore was rust. I spent a couple of weeks scrubbing the bore and found there was an accurate rifle in there. After following the AMTU accurizing procedure, I had a rifle that would shoot .5 MOA with Remington Match .308.
Now my M1A has its own pages in the binder. On it I note the number of rounds, the source of the ammo (reloads, factory and what type) and if any of the shooting was rapid fire. I also note when it is cleaned, when it is disassembled (M1As are sensitive to disassembly) and what the groups it shoots are like. I'm at 3,278 rounds since building it, and it is still more accurate than I am.
I do the same with my match AR-15s, and I'll tell you that the Eagle Arms is close to "due for a new barrel" while the Colt is holding up well. The Eagle, on its second barrel, is at 9,713 rounds, and if I were using it for NRA High Power competition I'd probably have a new barrel already. It "only" shoots .75 to one inch, but it is showing signs of shifting zero when switching from one load to another or one bullet weight to another, which it did not do when new. The Colt, while more sensitive about what ammo it likes, has not changed group sizes or zero with the individual loads.
The most detailed record-keeping is the "legal standard," or what police marksmen should do. Every shot is logged. Time, date, weather, range, ammo, rifle, position--all are noted. The group size is noted, or the target is saved and inserted in the log book. A record of the first, or cold and clean, shot is kept, and often that target is saved. Why? Because first, lives can be at stake. And second, lawyers will be involved.
Law enforcement personnel have many details to record. First, is the rifle actually zeroed? Is the officer properly trained, and has he kept up his skills? Is the new batch of ammo the same as the old batch? Following every question is the demand, "Prove it."
As for the cold and clean zero, that is likely to be the first shot needed. And there is no point in zeroing a rifle at the range on a warm summer day, then needing it in the dead of winter and not knowing if the rifle shoots to the same point of impact. That's why if you could see police marksmen at the range, you'd see them shivering on a January day on their day off, testing their rifle.
When there is an officer-involved shooting, all these questions will be asked--by the investigators, perhaps the grand jury and opposing counsel. Former Marines will be familiar with this level of detail, as each recruit starts with a log book and fills it out every single time he (or she) goes to the range. Woe to the Marine who can't show the PMI the results of every last shot fired.
The Legal Standard is best done in a bound book so it can't be altered (if you are really in a position to need it as proof in a legal matter) and the targets witnessed, signed and kept in a secure folder with the book.
How much record-keeping detail do you need? That depends on what you expect to learn and how much work you're willing to go through. At the simplest, you should keep a rough guide of how many rounds you've fired and the dates they were fired.
You should also keep track of the cleanings and how thorough a cleaning the gun received. (Much of my gunsmithing work came from shooters who had lost track of cleaning and presented me with an incredibly dirty or rusty rifle.)
If you are a high-volume shooter, tracking round count and accuracy will let you know when it is time to change barrels. If you plan on hunting someplace inaccessible or exotic, you'll want to test your rifle in all weather and keep notes on its performance.
Competition shooters need more detail. Reloaders also need detail. What powder, primer, bullets and cases did you use? What powder weight, what overall length, how were the primers seated? What accuracy results did you get, and what velocities did the chronograph turn up? What rifle did you use, what rest or rests, what was the range, the weather conditions, the wind?
To store the information, at the simplest, a file card for each rifle will do. On the front, record the start date, description and serial number. Then each time you shoot,
note the date and the number of rounds. By the time you've filled the card, you probably will need a new barrel.
Another way is the loose-leaf binder, with a page for each rifle. The larger page gives you more room, and it is easy to add pages.
As for the spreadsheet on a computer, one of these days I guess I'll be more comfortable with it, but for now I'll stick with my loose-leaf binders and ledger.