Maximum Point Blank Range: What distance should you zero your rifle for?January 10th, 2011 at 4:31
Comparison by Winchester Ballistics of various weight .308 and .223 bullet trajectories fired out of a rifle zeroed at 25 yards. Click to Embiggen.
It’s a common question: what distance should you zero your rifle for? Many hunters I know simply zero their rifles at whatever distance is available at their local range. But is this the ideal distance to have your scope set at? The answer varies depending on the caliber your rifle is chambered in and what game you are pursuing.
Let’s talk for a bit about what Maximum Point Blank Range (MPBR) is. In a nutshell, the MPBR is the maximum range at which you can aim your rifle directly at any target within that distance and be reasonably assured that your round will hit. What that distance is depends on the size of your target, the round you are firing, and the configuration of your rifle.
On medium sized North American game animals, the size of the vital area is generally 10 inches in diameter. That gives you 5 inches of bullet rise above the sight height and another 5 inches of drop below the sight height.
To figure the best distance to have your scope dialed on at, you’ll need to know your rifle and chosen ammunition well, and you’ll need to be able to do a little bit of math. But to help you out, there are online ballistic calculators available from Winchester and a very comprehensive calculator over at JBM Ballistics. In general, you’ll need to know the ammunition you are using including the bullet weight as well as the muzzle velocity it achieves in your firearm. If possible, it helps to know the bullet length and the ballistic coefficient. Both Winchester and JBM ballistics have fairly comprehensive libraries with all of this information included with particular Winchester cartridges or bullets in the case of JBM Ballistics. The final piece of information you’ll need is the height of the center line of your scope over the rifle bore. In most modern firearms this ranges from about an inch up to around 2.5 inches.
If you’re using a .308 caliber rifle, depending on your load, you’ll have a maximum point blank range of just over 300 yards. A 150 grain .308 caliber Barnes XLC boattail bullet will top out with 4.8 inches of rise at 150 yards and be dead on at 300 yards. This gives you “minute of deer” accuracy out to nearly 350 yards, meaning that with the crosshairs of your scope centered on the vital area of a deer, you will be assured of a solid hit at any distance out to 350 yards.
For most modern rifles, I usually recommend zeroing at a distance between 100 and 300 yards. The higher the ballistic coefficient of the bullet and the faster it is traveling when it leaves the muzzle, the longer the distance you can expect to be able to have your rifle zeroed for. Obviously, if you have a .22 caliber squirrel gun, the size of your target is much smaller and consequently your MPBR will be much shorter, usually only 50 or 100 yards. Small fast varmint rounds may have a high muzzle velocity, but due to their light weight and low ballistic coefficient, they lose speed fast. Most varmint rifles will do well to be zeroed at distances between 200 and 300 yards. For larger calibers capable of making shots out past 600 yards, especially some of the larger .30 caliber belted magnums, you can reasonably zero your scope and rifle for 400 yards and beyond.
Not many people have access to a 300 yard range, but with the help of a a ballistic table, you can calculate exactly how high or low the round should impact at any distance. The .308 load we mentioned earlier has 4.8 inches of rise at 150 yards, but what if you only have access to 25 and 100 yard ranges? You can get the rifle on paper by zeroing it at 25 yards, and then fine tune it until your group is centered at 3.9 inches high at 100. A bullet fired from a rifle starts out anywhere from 1″ to as much as 2.5″ below the sight height. For a rifle zeroed at 25 yards this means that the bullet must climb fairly steeply, and of course it will continue to climb for another hundred yards or so before reaching the apex and beginning to descend. For this particular load, the initial 25 yard zero should get you roughly on target at 300 yards. By confirming that your rounds are hitting 3.9 inches high at 100 yards you’ll get the rifle much closer to being precisely on target at 300.
I don’t know of any hunters running bench rest guns capable of putting a 5 shot group inside the diameter of a quarter at 600 yards. If you’re running a traditional .30-30 in the thick South Texas brush, a 100 yard zero is probably just fine. But for most other situations, it only makes sense to zero your scope and rifle combination for the Maximum Point Blank Range, which depends on your quarry and the caliber of your rifle.