First, a big thanks for all you do to educate and enlighten us! My day is not complete until I have had my SurvivalBlog fix (one of my good habits!).
I whole-heartedly support your gun is a tool analogy, and that having just one gun is like having just one tool in the box. Where we would differ is in how to build a suitable battery of firearms to fill most needs – much like a plumber’s tool box will look different from a auto mechanic’s. Under the cover of YMMV, those of you who have escaped to the American Redoubt, will have different needs from those of us stuck in more populated areas. The need for a precision shooting / hunting rifle doesn’t play in my semi-rural area (although that doesn’t mean you can have my Remington 788 in .308 Winchester). We also may have different physical capabilities that make some options unsuitable. Most of what I discuss below is an expansion or re-ordering of your recommended battery:
1) Shotgun. While one gun is never enough, a good shotgun is the multi-tool of the firearms world. With the right barrel/ammunition combination you cover small game, upland birds, waterfowl, defense, and medium game. Add a rifled slug barrel and sabots, and this list expands to include any large game or dangerous animal in North America out to 150 yards (see this month’s American Rifleman magazine for a look at the performance of the latest generation of slugs). I am partial to your recommendation of the 12 gauge Remington 870, but I have also had great results with the less expensive Mossberg 500. I would further expand the recommendation to include 20 gauge guns for those folks that have trouble with weight or recoil.
Everyone should own at least one shotgun, even if it is a single shot. Just view this video of Clint Smith running an H&R/NEF to see what a trained person could do with a single shot.
2) Defensive Handgun. To me concealment is the key factor of the handgun; otherwise I would walk around with a shotgun or battle rifle slung on my shoulder. I understand your (and my Father’s) love of the .45 ACP, but the world of defensive handguns no longer begins or ends with calibers that start with 4. Modern ballistics have advanced viable weapon status down to even the lowly .380. I also buy-in to the thought (my undying admiration of John Moses Browning not withstanding) that the best handguns ever made are being made today. That means there are scores of guns, from a good dozen manufacturers that would fill this need nicely. The most important consideration is finding a gun that fits you and your wallet. Additional note: revolvers still work!
3) .22 Rifle. I would greatly expand the list of options here. When you look at the main uses of this weapon (game getting, practice, and pest control) even a single shot would fill the bill. Think about your dad’s old Winchester 67. Also, my experience with both the Mossberg Plinkster and the Remington 597 would have me put them in line with the Marlin 60 for those on a budget.
4) High Powered Rifle. I define this as anything that can reach out and touch something in the 250+ yard range. This includes your battles rifles (with additions below), your precision shooting / hunting rifle, a myriad of surplus military guns (Enfield, Springfield M1903, Mosin Nagant, K31 Swiss, Arisaka, Carcano…), the ubiquitous lever gun, and even a single shot Handi-rifle. If a battle rifle is your choice for this category you can’t go wrong with any of your .308 or 7.62×39 recommendations. But, I will commit the heresy of adding .223/5.56 to the list. I would include not only most M4geries, but the Ruger Mini-14 or Mini-30 and even the Kel-Tec SU would work as budget alternatives.
I will end just as you did: “Be sure that you also budget for training ammunition and instruction, regardless of your choice in guns. Tools without training are useless.” – Terry P.