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46-429: The Farquhar-Hill is a long recoil operated semi-automatic rifle with rotary bolt locking. It was .303 British caliber and fed from a 19-round drum magazine. Magazine variations included a 10-round truncated cone and a 65-round drum. It has a muzzle velocity of 732 m/s (2,400 ft/s) and is sighted to 1,500 yd (1,370 m). Some models of the rifle have a bayonet lug for an experimental shortened version of

92-426: A 1-gram (15- grain ) projectile was accelerated to velocities exceeding 9,000 m/s (30,000 ft/s) at Sandia National Laboratories in 1994. The gun operated in two stages. First, burning gunpowder was used to drive a piston to pressurize hydrogen to 10,000  atm (1.0 GPa). The pressurized gas was then released to a secondary piston, which traveled forward into a shock-absorbing "pillow", transferring

138-420: A 27% mean loss in momentum. Energy, in most cases, is what is lethal to the target, not momentum. In conventional guns, muzzle velocity is determined by the quantity of the propellant , its quality (in terms of chemical burn speed and expansion), the mass of the projectile, and the length of the barrel. A slower-burning propellant needs a longer barrel to finish its burn before leaving, but conversely can use

184-484: A bullet fired from such a gun on the surface of the body would leave its gravitational field; however, no arms are known with muzzle velocities that can overcome Earth's gravity (and atmosphere) or those of the other planets or the Moon. While traditional cartridges cannot generally achieve a Lunar escape speed (approximately 2,300 m/s [7,500 ft/s]) or higher due to modern limitations of action and propellant ,

230-415: A diurnal or semidiurnal (twice-daily) cycle caused by global atmospheric tides . This effect is strongest in tropical zones, with an amplitude of a few hectopascals, and almost zero in polar areas. These variations have two superimposed cycles, a circadian (24 h) cycle, and a semi-circadian (12 h) cycle. The highest adjusted-to-sea level barometric pressure ever recorded on Earth (above 750 meters)

276-480: A heavier projectile. This is a mathematical tradeoff. A faster-burning propellant may accelerate a lighter projectile to higher speeds if the same amount of propellant is used. Within a gun, the gaseous pressure created as a result of the combustion process is a limiting factor on projectile velocity. Consequently, propellant quality and quantity, projectile mass, and barrel length must all be balanced to achieve safety and to optimize performance. Longer barrels give

322-410: A location on Earth 's surface ( terrain and oceans ). It is directly proportional to the mass of air over that location. For numerical reasons, atmospheric models such as general circulation models (GCMs) usually predict the nondimensional logarithm of surface pressure . The average value of surface pressure on Earth is 985 hPa. This is in contrast to mean sea-level pressure, which involves

368-427: A pressure of about 2 atmospheres (1 atm of air plus 1 atm of water). Conversely, 10.3 m is the maximum height to which water can be raised using suction under standard atmospheric conditions. Low pressures, such as natural gas lines, are sometimes specified in inches of water , typically written as w.c. (water column) gauge or w.g. (inches water) gauge. A typical gas-using residential appliance in

414-446: A source of energy for cycling of the bolt with a stationary barrel, simplifying design and making it potentially more accurate and reliable. The design was refined and then tested by British Army on several occasions. This rifle was initially chambered for the new ".303 rimless" round, designed by necking up the 7.65x53mm Belgian Mauser case and loading it with British-issue Mk.VII bullet of .303 caliber. Later on this experimental loading

460-424: A standard lapse rate) associated with reduction of sea level from high elevations. The Dead Sea , the lowest place on Earth at 430 metres (1,410 ft) below sea level, has a correspondingly high typical atmospheric pressure of 1,065   hPa. A below-sea-level surface pressure record of 1,081.8 hPa (31.95 inHg) was set on 21 February 1961. The lowest non-tornadic atmospheric pressure ever measured

506-401: A substantial distance and even hit a target before a nearby observer hears the "bang" of the shot. Projectile speed through air depends on a number of factors such as barometric pressure , humidity , air temperature and wind speed . Some high-velocity small arms have muzzle velocities higher than the escape speeds of some Solar System bodies such as Pluto and Ceres , meaning that

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552-508: A variety of reasons. Muzzle velocity Muzzle velocity is the speed of a projectile ( bullet , pellet , slug , ball / shots or shell ) with respect to the muzzle at the moment it leaves the end of a gun 's barrel (i.e. the muzzle ). Firearm muzzle velocities range from approximately 120 m/s (390 ft/s) to 370 m/s (1,200 ft/s) in black powder muskets , to more than 1,200 m/s (3,900 ft/s) in modern rifles with high-velocity cartridges such as

598-458: Is caused by the gravitational attraction of the planet on the atmospheric gases above the surface and is a function of the mass of the planet, the radius of the surface, and the amount and composition of the gases and their vertical distribution in the atmosphere. It is modified by the planetary rotation and local effects such as wind velocity, density variations due to temperature and variations in composition. The mean sea-level pressure (MSLP)

644-503: Is instead reported in kilopascals. In the US weather code remarks, three digits are all that are transmitted; decimal points and the one or two most significant digits are omitted: 1,013.2 hPa (14.695 psi) is transmitted as 132; 1,000 hPa (100 kPa) is transmitted as 000; 998.7   hPa is transmitted as 987; etc. The highest sea-level pressure on Earth occurs in Siberia , where

690-518: Is susceptible to explosion. While this can be mitigated with safety precautions, railguns eschew the need for such measures altogether. Even the projectile's internal charges may be eliminated due to the already high velocity. This means the projectile becomes a strictly kinetic weapon. The United States Army defines different categories of muzzle velocity for different classes of weapons: Barometric pressure Atmospheric pressure , also known as air pressure or barometric pressure (after

736-460: Is the atmospheric pressure at mean sea level . This is the atmospheric pressure normally given in weather reports on radio, television, and newspapers or on the Internet . The altimeter setting in aviation is an atmospheric pressure adjustment. Average sea-level pressure is 1,013.25 hPa (29.921 inHg; 760.00 mmHg). In aviation weather reports ( METAR ), QNH is transmitted around

782-431: The .220 Swift and .204 Ruger , all the way to 1,700 m/s (5,600 ft/s) for tank guns firing kinetic energy penetrator ammunition. To simulate orbital debris impacts on spacecraft, NASA launches projectiles through light-gas guns at speeds up to 8,500 m/s (28,000 ft/s). FPS (feet per second) and MPH (miles per hour) are the most common American measurements for bullets. Several factors, including

828-465: The Siberian High often attains a sea-level pressure above 1,050 hPa (15.2 psi; 31 inHg), with record highs close to 1,085 hPa (15.74 psi; 32.0 inHg). The lowest measurable sea-level pressure is found at the centres of tropical cyclones and tornadoes , with a record low of 870 hPa (12.6 psi; 26 inHg). Surface pressure is the atmospheric pressure at

874-408: The barometer ), is the pressure within the atmosphere of Earth . The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325  Pa (1,013.25  hPa ), which is equivalent to 1,013.25 millibars , 760   mm Hg , 29.9212   inches   Hg , or 14.696   psi . The atm unit is roughly equivalent to the mean sea-level atmospheric pressure on Earth; that is,

920-1339: The troposphere , the following equation (the barometric formula ) relates atmospheric pressure p to altitude h : p = p 0 ⋅ ( 1 − L ⋅ h T 0 ) g ⋅ M R 0 ⋅ L = p 0 ⋅ ( 1 − g ⋅ h c p ⋅ T 0 ) c p ⋅ M R 0 ≈ p 0 ⋅ exp ⁡ ( − g ⋅ h ⋅ M T 0 ⋅ R 0 ) {\displaystyle {\begin{aligned}p&=p_{0}\cdot \left(1-{\frac {L\cdot h}{T_{0}}}\right)^{\frac {g\cdot M}{R_{0}\cdot L}}\\&=p_{0}\cdot \left(1-{\frac {g\cdot h}{c_{\text{p}}\cdot T_{0}}}\right)^{\frac {c_{\text{p}}\cdot M}{R_{0}}}\approx p_{0}\cdot \exp \left(-{\frac {g\cdot h\cdot M}{T_{0}\cdot R_{0}}}\right)\end{aligned}}} The values in these equations are: Atmospheric pressure varies widely on Earth, and these changes are important in studying weather and climate . Atmospheric pressure shows

966-416: The vapour pressure is equal to the atmospheric pressure around the liquid. Because of this, the boiling point of liquids is lower at lower pressure and higher at higher pressure. Cooking at high elevations, therefore, requires adjustments to recipes or pressure cooking . A rough approximation of elevation can be obtained by measuring the temperature at which water boils; in the mid-19th century, this method

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1012-451: The Earth's atmospheric pressure at sea level is approximately 1 atm. In most circumstances, atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. As elevation increases, there is less overlying atmospheric mass, so atmospheric pressure decreases with increasing elevation. Because the atmosphere is thin relative to

1058-443: The Earth's radius—especially the dense atmospheric layer at low altitudes—the Earth's gravitational acceleration as a function of altitude can be approximated as constant and contributes little to this fall-off. Pressure measures force per unit area, with SI units of pascals (1 pascal = 1 newton per square metre , 1   N/m ). On average, a column of air with a cross-sectional area of 1 square centimetre (cm ), measured from

1104-400: The US is rated for a maximum of 1 ⁄ 2  psi (3.4 kPa; 34 mbar), which is approximately 14 w.g. Similar metric units with a wide variety of names and notation based on millimetres , centimetres or metres are now less commonly used. Pure water boils at 100 °C (212 °F) at earth's standard atmospheric pressure. The boiling point is the temperature at which

1150-503: The atmospheric pressure at a given altitude. Temperature and humidity also affect the atmospheric pressure. Pressure is proportional to temperature and inversely related to humidity, and both of these are necessary to compute an accurate figure. The graph on the right above was developed for a temperature of 15 °C and a relative humidity of 0%. At low altitudes above sea level, the pressure decreases by about 1.2 kPa (12 hPa) for every 100 metres. For higher altitudes within

1196-564: The bayonet pattern 1907 of the Lee-Enfield Mark III rifle. The Farquhar-Hill was first patented in the UK in 1908 and in the United States in 1909. The key feature was an intermediate 'action' spring which stored recoil energy. Upon discharge, the barrel recoiled while still locked with the bolt, compressing the intermediate spring on recoil. Upon return of the barrel to the forward position,

1242-413: The bullet before it leaves the gun. Provided there's enough rifling in the barrel to adequately stabilize a particular round, there is no appreciable increase in precision with increasing barrel length. Longer barrels make it easier to aim if using iron sights, because of the longer sight radius, and with the right propellant load they can increase muzzle velocity, which gives a flatter trajectory and reduces

1288-408: The energy from the piston to the projectile on the other side of the pillow. This discovery might indicate that future projectile velocities exceeding 1,500 m/s (4,900 ft/s) have to have a charging, gas-operated action that transfers the energy, rather than a system that uses primer, gunpowder, and a fraction of the released gas. A .22 LR cartridge is approximately three times the mass of

1334-501: The energy stored in the intermediate spring cycled the bolt back and forth, extracting and ejecting the spent case and feeding a fresh round into the now stationary barrel. The main goal was to achieve smooth and reliable cycling, but the design was very complicated and thus badly suited for a military firearm. By 1911, Farquhar and Hill revised their rifle, changing its source of energy from barrel recoil to more convenient gas operated action. The new weapon also used an intermediate spring as

1380-447: The expanding gas ceases to propel the bullet forth. When a bullet is fired from a handgun with a 2-inch (51 mm) barrel, the bullet only has a 2-inch (51 mm) "runway" to be spun before it leaves the barrel. Likewise, it has only a 2-inch (51 mm) space in which to accelerate before it must fly without any additional force behind it. In some instances, the powder may not have even been fully burned in guns with short barrels. So,

1426-492: The extrapolation of pressure to sea level for locations above or below sea level. The average pressure at mean sea level ( MSL ) in the International Standard Atmosphere ( ISA ) is 1,013.25 hPa, or 1 atmosphere (atm), or 29.92 inches of mercury. Pressure (P), mass (m), and acceleration due to gravity (g) are related by P = F/A = (m*g)/A, where A is the surface area. Atmospheric pressure is thus proportional to

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1472-402: The force of the gas pressure behind it, and from that point, the velocity of the bullet would decrease. Rifled barrels have spiral twists carved inside them that spin the bullet so that it remains stable in flight, in the same way an American football thrown in a spiral will fly in a straight, stable manner. This mechanism is known as rifling . Longer barrels provide more opportunity to rotate

1518-487: The limitations noted above. With these railguns, a constant acceleration is provided along the entire length of the device by means of the electromagnetic pulse. This greatly increases the muzzle velocity. Another significant advantage of railguns is not requiring explosive propellant. The result of this is that a ship will not need to transport propellant and that a land-station will not have to maintain an inventory of it either. Explosive propellant, stored in large quantities,

1564-421: The mean (average) sea level to the top of Earth's atmosphere, has a mass of about 1.03 kilogram and exerts a force or "weight" of about 10.1 newtons , resulting in a pressure of 10.1 N/cm or 101   kN /m (101 kilopascals, kPa). A column of air with a cross-sectional area of 1   in would have a weight of about 14.7   lbf , resulting in a pressure of 14.7   lbf/in . Atmospheric pressure

1610-474: The muzzle velocity of a 2-inch (51 mm) barrel is less than that of a 4-inch (100 mm) barrel, which is less than that of a 6-inch (150 mm) barrel. Large naval guns will have high length-to-diameter ratios, ranging between 38:1 to 50:1. This length ratio maximizes the projectile velocity. There is much interest in modernizing naval weaponry by using electrically powered railguns , which shoot projectiles using an electromagnetic pulse. These overcome

1656-410: The need to adjust for range. A bullet, while moving through its barrel, is being pushed forward by the gas expanding behind it. This gas was created following the trigger being pulled, causing the firing pin to strike the primer , which in turn ignited the solid propellant packed inside the bullet cartridge , making it combust while situated in the chamber . Once it leaves the barrel, the force of

1702-447: The projectile in question. This may be another indication that future arms developments will take more interest in smaller caliber rounds, especially due to modern limitations such as metal usage, cost, and cartridge design. In a side-by-side comparison with the .50 BMG (43 g), the 15 gr (1 g) titanium round of any caliber released almost 2.8 times the energy of the .50 BMG (1 g at 10 000 m/s = 50 000 joules), with only

1748-407: The propellant force more time to work on propelling the bullet. For this reason longer barrels generally provide higher velocities, everything else being equal. As the bullet moves down the bore, however, the propellant's gas pressure behind it diminishes. Given a long enough barrel, there would eventually be a point at which friction between the bullet and the barrel, and air resistance, would equal

1794-439: The type of firearm, the cartridge, and the barrel length, determine the bullet's muzzle velocity. For projectiles in unpowered flight , its velocity is highest at leaving the muzzle and drops off steadily because of air resistance . Projectiles traveling less than the speed of sound (about 340 m/s (1,100 ft/s) in dry air at sea level ) are subsonic , while those traveling faster are supersonic and thus can travel

1840-483: The weight per unit area of the atmospheric mass above that location. Pressure on Earth varies with the altitude of the surface, so air pressure on mountains is usually lower than air pressure at sea level. Pressure varies smoothly from the Earth's surface to the top of the mesosphere . Although the pressure changes with the weather, NASA has averaged the conditions for all parts of the earth year-round. As altitude increases, atmospheric pressure decreases. One can calculate

1886-591: The world in hectopascals or millibars (1 hectopascal = 1 millibar), except in the United States , Canada , and Japan where it is reported in inches of mercury (to two decimal places). The United States and Canada also report sea-level pressure SLP, which is adjusted to sea level by a different method, in the remarks section, not in the internationally transmitted part of the code, in hectopascals or millibars. However, in Canada's public weather reports, sea level pressure

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1932-543: Was "Rifle. .303 inch, Pattern 1918". However, the war ended before production facilities were allocated, and manufacture of Farquhar–Hill rifles was cancelled in 1919. During the 1920s and early 1930s Farquhar redesigned this rifle into a lightweight machine-gun fed from top-mounted pan magazines. On several occasions the British Army tested this machine gun, known as the Beardmore-Farquhar but ultimately rejected it for

1978-551: Was 1,084.8 hPa (32.03 inHg) measured in Tosontsengel, Mongolia on 19 December 2001. The highest adjusted-to-sea level barometric pressure ever recorded (below 750 meters) was at Agata in Evenk Autonomous Okrug , Russia (66°53'   N, 93°28'   E, elevation: 261 m, 856 ft) on 31 December 1968 of 1,083.8 hPa (32.005 inHg). The discrimination is due to the problematic assumptions (assuming

2024-439: Was 870 hPa (0.858 atm; 25.69 inHg), set on 12 October 1979, during Typhoon Tip in the western Pacific Ocean. The measurement was based on an instrumental observation made from a reconnaissance aircraft. One atmosphere (101.325 kPa or 14.7 psi) is also the pressure caused by the weight of a column of freshwater of approximately 10.3 m (33.8 ft). Thus, a diver 10.3 m under water experiences

2070-576: Was discarded in favor of the standard issue .303 British ammunition. After several trials, including troop trials at the Front, and some use by observers in aircraft, in 1918 the Farquhar–Hill rifle was found to be suitable for military use and an official request was issued for procurement of as many as 100,000 Farquhar–Hill rifles. Official nomenclature assigned to the military Farquhar–Hill rifle in August 1918

2116-444: Was used by explorers. Conversely, if one wishes to evaporate a liquid at a lower temperature, for example in distillation , the atmospheric pressure may be lowered by using a vacuum pump , as in a rotary evaporator . An important application of the knowledge that atmospheric pressure varies directly with altitude was in determining the height of hills and mountains, thanks to reliable pressure measurement devices. In 1774, Maskelyne

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