With long range shooting becoming increasingly popular, the terminology associated with this particular shooting discipline is also becoming more commonly used. It is therefore worth a shooter's while being acquainted with the most important ballistic terms in order to understand key aspects of long range shooting.
The website www.gunsaddicts.com recently published a very insightful piece in this regard, and here follows a shorter version of the key terms discussed in their article.
Simply put, this is the path the bullet takes as it travels towards the target. Projectiles speeding through the atmosphere are affected by gravity and air resistance, with gravity pulling the bullets downward and air resistance causing them to continuously slow. This loss of speed, paired with gravity, causes them to drop faster and faster toward the earth, resulting in a parabolic curve in the bullet's path. Simple apps on a phone or computer can, when fed accurate information, calculate trajectory with admirable precision, enabling shooters to compensate and hit their target.
When a bullet exits the muzzle of a firearm, it does so at a certain speed, which is termed velocity. As it encounters air resistance, it immediately begins slowing, and it will continue to slow until it runs out of steam and its curving trajectory takes it to earth. Velocity plays a big part in how much energy a bullet carries to the target, and because every bullet continually sheds velocity, energy diminishes as velocity diminishes. In the hunting world, velocity is important for an additional reason: to reliably cause a bullet to expand, or mushroom. Without expansion bullets tend to poke a knitting-needle size hole, which kills much more slowly and less humanely. Knowing the specific velocity of a chosen bullet when it exits the muzzle of a particular rifle is also critical to accurately calculating its trajectory. While ammo boxes or manufacturers" websites often offer velocity specs that come close, nothing replaces actually measuring velocity as fired from your rifle, which is easily done with any decent-quality chronograph.
This term, usually abbreviated to "BC,"Â� refers to the aerodynamics of a bullet. A long, sleek bullet with a very pointy tip and a boat-tail base slips through the atmosphere much easier than a blunt-nosed, flat-base design; thus it maintains its velocity much more efficiently. Bullets with high BC's are critical to long-distance shooters: They have a flatter trajectory, drift less in the wind and maintain energy and expansion-causing velocity better. BC numbers are commonly represented by a decimalized portion of a whole; for instance a G1 BC of 0.370 could represent a common, somewhat blunt bullet; a G1 BC of 0.600 or higher is considered very good indeed in terms of aerodynamics. All of this, of course, also depends on the caliber and density of the bullet, as well as other factors.
As a bullet travels, any wind present exerts forces that cause it to drift. Most commonly, the drift is lateral, but in rare occasions ÃƒÂ¢Ã¢â€šÂ¬Ã¢â‚¬Â� such as when shooting parallel to a very steep mountainside with a stiff wind traveling up or down it, wind can actually push a bullet vertically. A crosswind that is perfectly perpendicular to the line of a bullet's travel is typically called a "full value"Â� wind, because it exerts the most possible wind drift. A wind straight in your face or from straight behind you is called "no value"Â� because it has no discernible effect on the path of the bullet.
Drop is closely related to trajectory. As air friction robs a bullet of its velocity and gravity exerts its irresistible pull, a bullet drops toward the earth. Compensating for it is a matter of calculating how much drop there will be at a whatever distance the target is, then holding over it by pointing the gun high, so that the bullet drops into the target.
Minute of angle
One MOA measures 1.047 inch at 100 yards, so let's just call it an inch. At 200 yards it's double that. At 700 yards, it's seven times that. While it's not exactly the same as an inch, it's close enough for practical purposes: At 1,000 yards 10 MOA measures 10.47 inches. Where MOA comes in really useful is in adjusting for hold at long range. For instance, shooters can either use a scope with a reticle that provides a one-MOA grid to hold over and off for drop and wind drift, or they can dial corrections into an MOA-marked target turret that adjusts the internal crosshairs, and then hold right on. The windage and elevation turrets on most scopes are marked in either MOA (with quarter-MOA positions, or four "clicks"Â� per MOA) or mils (we"ll get to that next). Dialing in MOA is much simpler than in inches. The great beauty of the MOA system is that, as a tiny slice of the 360-degree sphere in which you stand in the middle, an MOA is an MOA whether at 100 yards or at 650 yards. If the drop chart on your ballistic calculator calls for 19 MOA at 650 yards, dial in 19 MOA and shoot the target.
Like MOA, the milling system is based on an angular measurement rather than a linear measurement. Military shooters claim that it's superior to the MOA system. Basically, the mil system is used in much the same fashion as the MOA system, the main differences being that elevation and windage adjustment turrets on the scope are marked in mils and tenth-mils.
The term is an acronym for "data on previous engagements."Â� Many of the best long-range shooters keep a logbook in which they record conditions, shot distances and results every time they practice or compete, and those records can prove a valuable resource for later shoots.
This refers to atmospheric pressure, in essence air density, and thus the amount of friction it exerts on a projectile is strongly affected by temperature and altitude. Air density has a dramatic effect on velocity, which in turn affects how much bullet drop has to be compensated for.Experienced shooters can make a fairly effective guess at temperature, and anybody with a topo map can determine altitude. Plugging those basic numbers into a ballistic calculator will get a shooter close, but to get it just right a shooter will need to use a hand-held weather station such as one by Kestrel. It measures actual pressure, including the influence of temperature, altitude, weather fronts and so forth. Advanced Kestrels, such as those with on-board ballistic software, can be programmed with a shooter's cartridge, bullet and rifle's data, after which they"ll calculate and provide drop and wind holds based on actual, current conditions right at the shooter's position.
The full article can be seen at http://www.gunsaddicts.com/common-ballistic-terms-you-should-know/
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