There are multiple caliber combinations that can be shown to have effectively identical trajectories over the ranges of interest. For example, letís look at one manufacturerís catalog offerings. In this case the Hornady catalog shows several cartridge and bullet combinations that show very close to the same drop out to 500 yards.
We can see from the table that both the wind drift and trajectory for each of these six loads are within five inches at 500 yards. This means that the .223 Remington with the standard velocity Hornady 75 gr BTHP has the potential of forming the basis for off season practice out to at least 500 yards for cartridges as powerful as the venerable .375 H&H Magnum! Further, the .223 Remington has less than one-tenth of the recoil energy as does that heavy .375 load.
Alternatively, the 75 gr Hornady Superformance round in .223 Remington works for slightly flatter shooting variants in the .338 Winchester Magnum, the .325 Winchester Short Magnum, and the .300 Winchester Magnum cartridges.
Matching trajectories from catalog information and calculated drift numbers by no means places us home free. The serious shooter needs to assure that each of his rifles are sighted in under the same conditions and to the same point of impact. The sight-in isnít complete until the full battery is registered and sights adjusted to a common impact point at the longest range the shooter intends to hunt at. This last step may cause some divergence of an inch or two the 100 Ė 200 yard environment, but will assure that the trajectories are close enough at all ranges of interest.
The larger rifles are frequently used in dangerous game areas so the shooter becomes the one hunted often enough to be a consideration. This turnabout in roles evokes the well-founded admonition to practice with your rifle until you have an instinctive feel in shouldering, sighting and shooting a powerful rifle. How does this advice work with using as many as three different guns Ė one for practice, one for deer and elk, and the third for dangerous game territory?
We naturally want to mount optics that allow for quick, accurate shots in close. At the same time, we see that the cartridge is capable of some rather long shots. My Dadís compromise was to use a simple 4X fixed power scope. This was the most popular scope during that period largely because it did balance ease of target acquisition with reasonably precise aiming for large game out to 300-400 yards. He also practiced on jackrabbits. Most of his rabbit shooting was in the stalking mode, which meant that he had plenty of opportunities to get the crosshairs into the right spot on fast moving animals from a few yards out to much longer distances. Naturally he got spectacular feed back when the .375 Magnum connected with a running jackrabbit!Following the Paired Rifle concept means that you want the same optic mounted on your light recoiling rifle and that the top-level handling characteristics like action, stock type, length of pull, rifle center of gravity, and sweet spot for eye relief are the same. My fatherís experience with the fixed four-power scope suggests that a 3-9 power scope with a comfortable reticle will suffice provided that one practices enough at short ranges to become comfortable with getting the scope on target at the lowest setting. There will be time to reset the scope to the higher magnification for shots at ranges of greater than 75 or 100 yards. While the best answer to the basic rifle match is to custom build a set of two or three rifles that are the same except for the cartridge, this is likely also the most expensive option. Most of us wonít be able to spend the kind of money needed to exercise this one.
What compromises are available so that we can get the most with our limited budget? To get a better feeling for the compromises, letís think through the sequence of loading, shouldering, and firing our heavy rifle. The single most important act is bringing the rifle to the shoulder and looking through the sight. We want that to be the same independent of the rifle. This means that the stock, length of pull, and eye-relief need to be the same. Still at the top level is the sight picture. We want it to be the same whether it is the heavy or the light rifle. Further, when stock type, length of pull, rifle center of gravity, and sweet spot for eye relief, and trigger are the same, you wonít know whether you are shouldering your light-recoiling rifle or your shoulder crusher until after the trigger squeeze.
A subtle, but significant, issue is the length of the action. There are stories of folks getting into trouble with bolt action rifles because they failed to run the bolt over its full length of travel. For example, you will do a lot of shooting with the .223 and develop muscle memory for how far the bolt turns and how far back you need to pull to eject the spent cartridge and load the new round. A short action optimized for the .223 has a much shorter stroke than the magnum-length action needed for the .375 Magnum. The length of required bolt stroke may be a factor in your choice of paired rifles and cartridges.