There are many pragmatic variables when you are buying and collecting firearms. A logical gunny would carefully weigh the application that the firearm would be used for and pick the best value that works for that application.
Most of us gun-nut types completely ignore these pragmatic reasons to buy a gun, and we justify all our emotional choices with whatever reasons we can come up with. That is why the Judge, Desert Eagle and BFR exist. It is also the reason that there are eleventy-billion hunting calibers used on North American game.
Pragmatically speaking, if you wanted to assemble an arsenal that would never be used for shooting people or animals, the .22 Long Rifle would be all that you needed. You can shoot groups, plink, run-and-gun and whatever other shooting you like to do with a rimfire. You can stretch the little .22LR out to 100, 200 or even 300 yards and practice your practical marksmanship with wind and long ranges. You could assemble a great collection of .22 rifles, pistols and revolvers that are a blast to shoot, saving serious money on ammunition.
Once you add in hunting or self defense to your reasons to own a gun or guns, you start to complicate things. Shotguns and Rifles are best for shooting birds, deer and people. For home defense the best tool would be a rifle in .223 Remington/5.56 NATO. For hunting birds you of course need a shotgun, which would also work nicely for other animals and home defense. If you conceal carry for defense you need a handy pistol in a fighting caliber.
Here is a list of my current ideas for assembling an arsenal:
Of course 9mm and of course the GLOCK model 19. Honestly any 9mm that is GLOCK 19ish sized will work in the carry role. 9mm is the perfect handgun round. If you choose wisely you can have terminal ballistics as good as it gets in a handgun round, capacity will the best and training ammo will be nice and cheap.
This one is easy, an AR-15 in 5.56. 30 Rounds of terminally perfect and low penetrating rounds in an easy to handle, lightweight, modular platform. The AR is proving itself as the perfect man-killer as the choice of elite SWAT teams as well as uber cool military operators. In the home defense role any handly little rifle in .223 will do the trick. The ubiquitous pump-action shotgun falls short in this application due to excessive reload times, but it would more than suffice in a pinch.
If you are perfectly pragmatic, your practice gun would be a .22 version of your carry gun and your AR-15. You could even just add a rimfire conversion kit to your blasters, but then that wouldn't let you buy another gun for the safe. An alternative to the finicky ,22LR conversion is the legendary Ruger 22/45 in its many and optional configurations. The dedicated .22 LR AR-15 or a S&W M&P15-22 are both wonderful alternatives to a Atchisson style conversion system. A reliable rifle like the 10/22 or the Marlin 795 makes a very adequate trainer for sight alignment, sight picture and trigger control. If you were really hard core you could have an AR-15 in 9mm as a practice gun. Maybe even one that takes GLOCK mags like your carry gun.
Competition is like racing; you build the gun to the rules. This fact makes the competition gun very specific and usually not a good candidate for multitasking. We can all agree that a 25m pistol makes a terrible carry gun and that a home defense rifle is a very poor choice for shooting an across-the-course match. There is some opportunity for overlap here though. A 3-gun blaster may work fairly well as a carry gun or a home defense shotgun. Your skeet gun will do very well on birds with feathers.
Precision Long Range
While some do like to use an AR platform in this area most folks will have a bolt-action Savage or Remington. Pick one in.308 Winchester if you do not reload and in any caliber you like if you do handload. .260 Remington and 6.5 Creedmoor really shine once you push it out past 800 yards. Unless you have a switch-barrel gun this precision rifle would probably be a poor hunting rig, although an SWS could work for meat gathering in a pinch. (This seems to be a theme here).
Like competition guns, hunting guns can be very specific to a certain type of game. A .375 H&H double gun is not really good for much else. A good brush gun say in 30-30 could make a perfectly adequate home defense rifle, but there are better choices for that task. As we have said many times, the shotgun may be the most versatile platform available. A good, reliable shotgun can do duty as a bird gun, a deer rifle and a home defense long gun. There may be better choices for some of those roles, but the shotgun never is a bad choice. The AR-15 could argue its way into being another versatile hunting gun. Swap the upper for a 6.8 SPC II to hunt almost everything in North America. If that isn't enough thump the 7.62x39 and .300 Blackout are available for any work previously left to the 30-30 WCF. I dont know what one hunts with the .450 Bushmaster, the .458 SOCOM or the .50 Beowulf, but I am sure people use it to kill some critter. Hogs?
If you follow these guidelines you should have a very pragmatic and fairly versatile collection in your safe. You do have a safe, right?
One could argue that a practice gun is not needed, and if you do not hunt or shoot competition you could easily skip those pieces. You may not be allowed to carry a gun in your jurisdiction. You may have zero need or no place to practice long-range shooting. This brings us to a very interesting conclusion. If you have one gun, it should probably be an AR-15. You may persuade us it should be a shotgun from Remington or Mossberg, but I could put up a good argument against that.
Let us know what you think.