Chronograph Your Hunting Ammo, Even if You Don’t Handload
Shooters and hunters love to buy gear. All you need to prove that is the number of people who fork over money to go to a gun show or outdoor show. You are paying money to be advertised to by businesses who want to sell you stuff. And we love to go and be "sold" on things we may or may not need.
Some gear is essential, like an accurate rifle, reliable ammunition, or a good knife. Other gear is nice to have but less essential, like shooting sticks or a laser range finder. Then there is the gear that is little more than gimmicks and gadgets that range from unnecessary to completely worthless, but I will politely not cite examples here. When you previously perused the aisles of your local gun shop there is one thing you likely saw but maybe never thought to lay down money for that probably fits in one of the first two categories I mentioned: a chronograph.
If you are a handloader there is a decent chance you own a chronograph or have access to one. And why wouldn't you? After spending hours and hours toiling over the minutia of your homemade ammunition, you want to know exactly how consistent and what kind of performance you are getting.
You might be thinking, "I don't handload. I sight in my rifle at 100 yards and it groups well. Why do I need a chronograph?" Because the ballistics on the box of ammo will likely not match the ballistics of that ammo fired through your rifle.
Let's say you planned on hunting deer with your trusty high quality rifle chambered in .308 Winchester. You bought a few different boxes of ammo to see what groups the best and settled on Nosler 165 grain Ballistic Tip. You zeroed your high quality rifle with your high quality scope at 100 yards and you were able to shoot one inch groups with it off the bench. You're all set! A few weeks later the opening day of deer season arrived. You got to your spot bright and early and took in perhaps the greatest sunrise in history. 45 minutes later you spotted the biggest trophy buck your eyes have ever witnessed in person. Being smart, you ranged the area before you hunted so you would know where to hold your bullet drop compensating reticle. The deer stood near a tree you had previously measured with a laser range finder at 375 yards. You got behind your rifle and took the shot you were so prepared for.
And you missed.
You saw an impact in the ground under the body of the buck. He got spooked and disappeared over the hill and out of site just as you found him in your scope again. It was a long shot, but well within the range of your trusty .308. Your rifle was zeroed. It's a tack driver. You even had your super handy ballistics calculator on your smart phone tell you where to hold for the shot. You couldn't understand, what went wrong?
If you didn't flinch or get a case of the suddenly infectious "buck fever," the velocity you plugged into your ballistics calculator was probably off. The Nosler Ballistic Tips I mentioned in the the hypothetical situation listed a muzzle velocity of 2800 feet per second. Nosler makes fantastic cartridges and I don't doubt that the rifle they measured ballistics with did indeed achieve that velocity. As a handloader, that would be a pretty ambitious speed to achieve for a 165 grain bullet out of a .308 Win and without a really long barrel I wouldn't even try. Most 150 grain bullets would probably be in the neighborhood of 2850 fps.
You may have noticed I wasn't specific about what rifle was used in my hypothetical situation. I called it a "trusty, high quality rifle." I intentionally left that detail out because it was a factor I previously left out. I What if that .308 Win rifle was a 16 inch scout rifle, or a AR carbine instead of one with a 22-inch barrel? Velocity will be reduced with a shorter barrel.
When I plugged in these numbers into the Strelok app on my smart phone, at 2800 fps the shot would need a vertical correction of 22.05 inches. But if your rifle shoots this cartridge at 2550 fps, your correction will be off by around five inches. That could cost you if you are taking a long shot. This is why I like running store bought ammo over a chronograph. You will have a better idea how that ammo shoots out of your rifle.
Rifleshooter.com posted the results of an interesting experiment they did with various 7.62 NATO rounds with a rifle they cut down one inch at a time, from 28 to 16.5 inches. The difference in muzzle velocity was as high as 283 fps from. Velocity lost per inch of barrel was in the neighborhood of 23 fps.
Bullets start dropping quickly after about 200 yards. If your zero is 100 yards this is even more complicated. At 100 yards the bullet is still climbing. At 200 yards the bullet is dropping. Plus, being closer to a long range target, the amount of correction you need to make is significantly less than if you are zeroed at 100 yards. If you're trying to hit something in the 400-500 yard range, it is even more important to know what the actual velocity is.
If you are positive you won't be taking a shot is over 200 yards, you can zero your rifle at 100 yards and be pretty confident that you'll hit the vital area of a deer regardless of bullet velocity. But if you are hunting in some pretty wide open spaces, spending $100 - $150 on a chronograph could be very well worth it. Or check with your buddies or your gun club. They may have a chronograph you can borrow. Just make sure you shoot over the chronograph, not through the chronograph.