The greatest versatility comes from handloading. Handloaded, a moderate capacity cartridge, between 6.5 and .30 caliber, is not only an extremely useful general purpose big game choice, but can also be used for small game, plinking, varminting, and is appropriate for a number of target shooting challenges.
The rifle and how its set up can either limit or enhance its versatility. Light short and handy is usually the hunter's friend, but if too light, holding steady becomes difficult, and recoil becomes challenging, and if too short, painful muzzle blast will turn you into a flincher. I'm partial to magazine fed bolt action rifles, but I wouldn't opt to carry my 20 pound target rifle up the side of a mountain if I were on a Dall sheep hunt. Then again, a 2X scout scope, so useful in the thick stuff against dangerous game, it's low magnification and thick cross hairs might prove to be a disadvantage when shooting at a distant prairie dog town.
If I was going to build my idea of the ultimate general purpose rifle, I would start with a good example of a standard length controlled round feed action, which is my preference, perhaps a Brno 600, or ZG-47, maybe a M-70 Winchester,a Ruger, or a commercial Mauser. Others might prefer a SAKO, Tikka, or a Remington. While the trigger doesn't need to be adjustable, I want it as free of creep and over travel as possible, with about a 3 pound let off. A two stage trigger, such as the ones made by Huber, are my preference. I believe there is a small advantage to cut rifling, so I'd choose a barrel from Kreiger, Bartlein, or Ron Smith. IMHO, a 22" barrel is a good compromise between too short and too long, so a barrel 22" #3 sporter should produce a decently balanced rifle finished to 22". I might choose a #2 contour for a 24-26" barrel and a #4 for a 20". Balance matters more than shaving pounds, and the shorter the light contoured barrel, the clubbier the rifle feels. The barrel steel I would choose is carbon steel, if for no other reason than because John Kreiger says it has better characteristics in the cold than stainless, and much of my time in the field is in the cold. I also have a preference for fast twist barrels, so I would go with a 1:8 in .30 caliber, and probably my cartridge of choice would be a .30/06. The fast twist results in less precession (yaw) when the bullet impacts the target, which enhances both the mechanical expansion of the bullet and its penetration on game. The disadvantage is that the fast twist isn't particularly good for shooting cast bullets, the barrel will foul badly and accuracy will be poor unless velocity is kept down to about 1200 fps and even then fouling might be an issue. If you're set on shooting cast, stick with a 1:10 twist for a .30 caliber rifle. I'd just use FMJ or inexpensive soft points loaded to cast bullet velocities for small game.
Now that we have an action, barrel and trigger, I'd assemble those and bed them into a good quality fiberglass stock. There is no such thing as a drop in precision fit, and attempting to do so with an expensive custom rifle, just to save a few dollars is counterproductive. Fiberglass isn't as luxurious as walnut, but it is stronger and more stable, and the price of high quality walnut is intimidating by comparison. I have a couple of McMillan's and like them, and would probably be inclined to stick with them. Robinson Composites is a Canadian company which by all reports produces a high quality stock, but last time I checked, only for round, M-700 type, actions. But if you want to build on a 700 Remington, or a clone, you should check them out. The importance of proper stock fit to the shooter cannot be overemphasized. My LOP is 13.5" but that is only part of the story. A quality recoil pad makes recoil far more tolerable. The height of the comb must be compatible with the sights on your rifle. Modern stocks are made so that you have a solid cheek weld with a scope sight mounted an inch and a half or so above the bore. This can be a problem if your irons are low forcing you to mash your cheek against the comb of the stock. When you touch it off, the recoil will cause your head to snap back, and if your rifle is a hard kicker, it will register between unpleasant and painful.
I like to shoot with the aid of a shooting sling, and the Safari Ching Sing is a good example of a shooting sling that is light weight, quick to use, and that doubles handily as a carry strap. My habit is to locate the front swivel on the radius of the forend tip, thus preventing the swivel stud from cutting groove out of my index finger when shooting without gloves on.
Now comes the question of sights. A general purpose rifle should be equipped with irons IMHO. I like ghost rings and rectangular posts. The thin rim, large aperture ghost ring produces sufficient precision for field shooting, and choosing a smaller aperture will most likely reduce the time it takes to make the shot rather than resulting in greater precision. The ghost ring is very fast. It is as simple as putting the front sight on the target and pressing the trigger, there is nothing to line up except for the position of the front sight on the target. By comparison, an open rear sight must be aligned with the front sight and then aligned with the target, which produces a complicated focusing problem because two or more objects at different distances cannot be held in simultaneous focus. The rectangular front sight produces a better index of elevation than any other type. Consider the rectangular post as you would a cross hair, the wide flat top is your horizontal wire, and the human eye being very good at finding the center of an object accurately and quickly determines the vertical wire. The disadvantage of the ghost ring and post though is that the ghost ring can seldom be left on the rifle when a scope is mounted. If this is perceived as a serious headache, perhaps an open sight is the better choice, and a quarter rib mounted express sight with a bead front sight would add a touch of elegance to an otherwise utilitarian piece. I like barrel band front sights, and either a scalloped Ruger or a NECG appeals to my eye, with the factory Brno my third choice. If a rectangular front sight is chosen, it should be either made from or faced in brass. Brass produces contrast on almost any natural background; appearing white on a dark target, or black on a light colored target.
A scope should be mounted in QD mounts. This can be useful if a high quality scope is used on a number of different rifles, or if a number of scopes are to be used on your one rifle, but more importantly, it allows you to have rapid access to your irons if the shooting situation demands it, or if your scope becomes damaged while in the field. A second scope can then quickly replace the damaged one, or your irons can be used for the duration . . . hope you've practiced. A good general purpose big game scope should be weighted towards the lower powers to take advantage of the wider field of view. A 1.5-5X, a 1.75-6X, a 2-7X, or a 2.5-8X are all viable choices. The 3-9Xs are popular, but by the time one get up to a 3.5-10X the scopes are physically large, and somewhat more delicate. Fixed power scopes are tougher, less complex inside, and smaller, with shorter eye pieces, but there might be an argument to be made that they don't have the versatility of a variable when mounted on a rifle that must fill may roles. The use of a pictinny rail style of base mount gives the shooter the greatest amount of flexibility for positioning the scope on his rifle, and if Larue type rings are chosen, the QD feature is retained without loss of zero. Not all mounting systems are suitable for use on all actions though.
The least important feature of the general purpose rifle is the cartridge it is chambered for. The .30/06 has become my favorite rifle cartridge, but a 6.5/06, a 270, or a .280, would all perform within the same performance envelope, with only minor differences in trajectory and terminal performance.
This is my idea of a general purpose centerfire rifle, it might not be yours. I believe this rifle could be had without the scope for about $5K, provided you didn't add extra embellishments like custom bottom metal, engraving, or presentation grade walnut. At a quick glance, this rifle might not appear to be much different than any off the shelf bolt gun that can be had for a fraction of the price, but as soon as its in your hands you'll see the difference.
