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October 19th, 2021

Four Good Tech Articles from Shooting Sports USA

Shooting Sports USA

NRA publication Shooting Sports USA (SSUSA) has thousands of articles online, all free for the reading. Many of these stories have been written by top competitors, including National and Olympic Champions. You will find SSUSA articles spotlighted every week on the NRA Competitive Shooting Facebook page. We recommend you bookmark that page as a valuable resource. Here are four notable SSUSA articles that have been featured on Facebook this month. Go to SSUSA.org to see even more current articles, with new content every day.

Shooting Sports USA Mirage Read optics scope

Here is an insightful, fairly lengthy 1850-word article about the phenomenon we call mirage. The article explains how and why mirage appears, how it can best be monitored, and how mirage can indicate both wind velocity and direction. Top competitors follow the adage “Mirage is your friend”, because mirage can often be the most important indicator of wind variables — sometimes even more important than wind flags. “The mirage is more sensitive than the flags since it has less inertia and momentum”, wrote Desmond T. Burke, in his book, Canadian Bisley Shooting, an Art and a Science.

Well worth reading, this SSUSA article talks about the properties of mirage. Here is a sample:

“Mirage — can make all the difference between a shot landing squarely in the X-ring or being victimized by an undetected downrange breeze. The true power of mirage is found in its ability to betray the subtlest of breezes downrange. Its fluid movement… can not only provide wind direction, but speed as well.

Typically, the ability to detect mirage is maximized on warm, sunny and sultry days. Expect mirage to be most pronounced in mid-morning or early afternoon, although it ignores these rules with regularity[.]

Mirage is extremely powerful at identifying winds of less than 12 mph, particularly those gentle breezes subtle enough to not even bother moving the flags.

When there is no wind, or a gentle head or tail wind, mirage will appear to be ‘bubbling’ directly up from the ground. Many call this ‘boiling’, and it is probably the easiest of all to detect.

As a general rule of thumb, when wind speed increases, overall height of the waves produced by the mirage is reduced. Large peaks and valleys in the waves mean that particular mirage is being driven by a very slight breeze. Conversely, crest size is reduced with wind speed, making it harder and harder to detect, until the mirage disappears entirely at somewhere around 12 miles per hour. In other words, the taller mirage‚Äôs waves appear, the slower the breeze.”

South Texas Mirage Reading article
Diagram from SouthTexasShooting.org.

Shooting Sports USA barrel maintenance break-in procedures Glen Zediker

Authored by the late Glen Zediker, this article covers barrel break-in procedures. It is particularly useful for dealing with factory barrels. We CAUTION readers — with outstanding, hand-lapped custom barrels from top barrel-makers, you may want to do very little break-in — clean sparingly and keep barrel heat low. Do NOT use abrasives aggressively. On our Krieger and Brux barrels, we simply wet-patched every 2-3 rounds for 20 rounds and the barrels shot superbly from the start with minimal fouling. But for factory barrels, a moderate break-in process may prove beneficial.

Zediker explains: “Lesser, lower-cost barrels are going to have more pronounced … imperfections within the bore[.] These imperfections are largely tool marks resulting from the drilling and rifling processes. And if it’s a semi-automatic, like an AR-15, there might be a burr where the gas port was drilled. The goal of break-in is to knock down these imperfections, thereby smoothing the interior surface.”

Shooting Sports USA pistol cartridge kaboom safety blowout

As one who has experienced a cartridge case-head blow-out with a 9mm pistol, this Editor is very conscious of the risks involved and the damage a blow-out can do to the pistol, to the magazine, and (worst of all) to the shooter. Even with new brass, the possibility of a case failure is always present. And even if the case remains intact, we’ve seen primer failures that create a dangerous jet back towards the pistol shooter. That’s why shooters should always employ protective eyewear whenever they shoot.

Shooting Sports USA revolver forcing cone repair damage

We love our wheelguns, but there’s no doubt that forcing cone damage can occur, particularly with hot loads and if your cylinder-to-barrel gap is excessive. This article explains how to inspect your revolvers, and how to mitigate the likelihood of forcing cone damage. The article also explains how to clean your revolvers properly. This is very important to avoid build-up of lead and powder residues.

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October 19th, 2021

How Altitude Affects Bullet Ballistics (Drag and Drop)

altitude ballistics zeiss LRP S5 318-50 FFP scope
Photo shows the new ZEISS LRP S5 318-50 first focal plane (FFP) scope.

“A bullet launched at a higher altitude is able to fly slightly farther (in the thinner air) for every increment of downward movement. Effectively, the bullet behaves as if it has a higher ballistic coefficient.”

It’s hunting season, and a good friend is heading to the high country of Colorado next week to pursue elk. He recently zeroed his rifle in California, at a range just a few hundred feet Above Mean Sea Level (AMSL). He wondered if the higher altitude in Colorado could alter his ballistics. The answer is a definite yes. However the good news is that free ballistics calculators can help you plot reliable drop charts for various shooting locations, high or low.

Suunto AltimeterThe question has been posed: “What effect does altitude have on the flight of a bullet?” The simplistic answer is that, at higher altitudes, the air is thinner (lower density), so there is less drag on the bullet. This means that the amount of bullet drop is less at any given flight distance from the muzzle. Since the force of gravity is essentially constant on the earth’s surface (for practical purposes), the bullet’s downward acceleration doesn’t change, but a bullet launched at a higher altitude is able to fly slightly farther (in the thinner air) for every increment of downward movement. Effectively, at higher altitudes, the bullet behaves as if it has a higher ballistic coefficient.

Forum member Milanuk explains that the key factor is not altitude, but rather air pressure. Milanuk writes:

“In basic terms, as your altitude increases, the density of the air the bullet must travel through decreases, thereby reducing the drag on the bullet. Generally, the higher the altitude, the less the bullet will drop. For example, I shoot at a couple ranges here in the Pacific Northwest. Both are at 1000′ AMSL (Above Mean Sea Level) or less. I’ll need about 29-30 MOA to get from 100 yards to 1000 yards with a Berger 155gr VLD at 2960 fps. By contrast, in Raton, NM, located at 6600′ AMSL, I’ll only need about 24-25 MOA to do the same. That’s a significant difference.

Note that it is the barometric pressure that really matters, not simply the nominal altitude. The barometric pressure will indicate the reduced pressure from a higher altitude, but it will also show you the pressure changes as a front moves in, etc. which can play havoc w/ your calculated come-ups. Most altimeters are simply barometers that read in feet instead of inches of mercury.”

As Milanuk states, it is NOT altitude per se, but the LOCAL barometric pressure (sometimes called “station pressure”) that is key. The two atmospheric conditions that most effect bullet flight are air temperature, and barometric pressure. Normally, humidity has a negligible effect. It’s important to remember that the barometric pressure reported on the radio (or internet) may be stated as a sea level equivalency. So in Denver (at 6,000 feet AMSL), if the local pressure is 24″, the radio will report the barometric pressure to be 30″. If you do high altitude shooting at long range, bring along a Kestrel, or remember to mentally correct the radio station’s pressure, by 1″ per 1,000 feet.

Trajectory of Bullet fired at Sea Level

Trajectory of Bullet fired at 20,000 feet

You can do your own experimental calculations using JBM Online Ballistics (free to use). Here is an extreme example, with two printouts (generated with Point Blank software), one showing bullet trajectory at sea level (0′ altitude) and one at 20,000 feet. For demonstration sake, we assigned a low 0.2 BC to the bullet, with a velocity of 3000 fps.

To learn more about all aspects of Exterior Ballistics, Hornady has a useful discussion of External Ballistics including the effects of altitude and temperature. To dig deeper, Sierra Bullets has a comprehensive Exterior Ballistics Resource Page with multiple sections from the Sierra Manual (4th and 5th Editions), including:

Section 3.0: Exterior Ballistic Effects on Bullet Flight
Section 3.1: Effects of Altitude and Atmospheric Conditions
Section 3.2: Effects of Wind
Section 3.3: Effects of Shooting Uphill or Downhill

Example from Section 3.0: “When a bullet flies through the air, two types of forces act on the bullet to determine its path (trajectory) through the air. The first is gravitational force; the other is aerodynamics. Several kinds of aerodynamic forces act on a bullet: drag, lift, side forces, Magnus force, spin damping force, pitch damping force, and Magnus cross force. The most important of these aerodynamic forces is drag. All the others are very small in comparison when the bullet is spin-stabilized.”

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October 19th, 2021

Parallax Explained — Nightforce Optics TECH TIP

Nightforce Optics Parallax Newsletter Scope Video

PARALLAX – What is it and Why is it important?

Nightforce Optics Parallax Newsletter Scope Video

What is Parallax?
Parallax is the apparent movement of the scope’s reticle (cross-hairs) in relation to the target as the shooter moves his eye across the exit pupil of the riflescope. This is caused by the target and the reticle being located in different focal planes.

Why is it Important?
The greater the distance to the target and magnification of the optic, the greater the parallax error becomes. Especially at longer distances, significant sighting error can result if parallax is not removed.

How to Remove Parallax
This Nightforce Tech Tip video quickly shows how to remove parallax on your riflescope.

While keeping the rifle still and looking through the riflescope, a slight nod of the head up and down will quickly determine if parallax is present. To remove parallax, start with the adjustment mechanism on infinity and rotate until the reticle remains stationary in relation to the target regardless of head movement. If parallax has been eliminated, the reticle will remain stationary in relation to the target regardless of eye placement behind the optic.

Nightforce Optics Parallax Newsletter Scope Video

This Parallax Discussion first appeared in the Nightforce Newsletter. Nightforce also offers a series of Informational Videos covering a variety of topics.

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