Palm Rest - An adjustable support for a target rifle extending downward from the forearm.
Parallax - The apparent movement of the target in relation to the reticle when the sniper moves his eye in relation to the ocular lens. When the target's image is not focused on the same focal plane as the telescope's reticle, parallax is the result. Current issue U.S. Army rifle telescopes have a field parallax adjustment that makes parallax error an insignificant factor when proper eye relief and stock weld are used.
Patch - 1. A piece of cloth used with a rod to clean the bore of a firearm. 2. A piece of paper wrapped around a lead bullet to prevent leading of the barrel and to improve the gas seal. 3. In muzzle loading firearms, the piece of cloth surrounding the bullet or ball to improve the gas seal.
Partial Resizing - In handloading, the resizing of the case neck, without pushing the shoulder back. Slight resizing of a section of the walls near the case head also occurs. Done by raising the full length resizing die a couple of turns in the press. Achieves virtually the same benefits as neck sizing, without the need for a special die. See Neck sizing.
Peep Sight - Rear sight in the form of an aperture mounted close to the shooter’s eye. Shooter “peeps” through the aperture, centring the front sight in the circle of the rear sight picture. The longer sight radius facilitates higher practical accuracy potential, and the system reduces the number of objects on which the eye must focus from three ( rear sight, front sight and target ) to two. Also known as aperture sight, receiver sight or ghost ring.
Piece - General term used for any firearm, e.g. “carrying a piece”. Originated from the term “fowling piece” which was a muzzle-loading shotgun.
Pierced Primer - Cartridge primer that has been pierced by the firing pin. Dangerous because the flame from the primer ( and even from the main powder charge jetting back though the flash hole ) can rush along the bolt tunnel to exit around the cocking piece, endangering the shooter’s eyes. Causes can be firing pin that is set to strike too deep, or too soft a primer.
Pitting - Term to describe small pits in the surface of gun metal ( usually in the bore ) caused by rust or corrosion from mercuric primers. Also see Barrel erosion / Barrel wear.
Plinking - The informal shooting at inanimate objects located at arbitrary or indefinite distances from the firing point.
Plinking Load - A handload which, for reasons of economy and reduced recoil, wear and tear, etc., is milder than the standard, and uses cheaper components, e.g. cast bullets. Normally used more to "keep in shape", than to do serious shooting.
Point Blank - A term especially related to hunting. The distance to which one can shoot at an animal, hitting in the target area, for example the vital ( heart/lung ) area, without any holdover. The mid-range trajectory and the bullet drop will both fall within the specified area. ( Click here for picture. )
Point Of Aim - The point on a target on which the sights are optically aligned when firing.
Point Of Impact - The point on which the bullet actually lands. By adjusting the sights, the point of impact can be made to coincide with the point of aim at a preselected distance; hence we say the rifle/sight/load combination is “zeroed” or “sighted in” at that range. Abbreviated POI.
Pointed Soft Point - (Bullet) abbr. PSP.
Port - 1. An opening in the wall of a barrel to allow gas to operate a mechanism or reduce sensible recoil. 2. An opening in a receiver to allow loading or ejection.
Powder / Gun Powder - The propellant, either smokeless ( nitro ) or black powder, used in cartridges or muzzle loaders, which burns to produce the expanding gases that force the bullet down the bore, propelling it to the target.
Powder Charge - See Charge.
Powder Funnel - A helpful accessory in handloading that facilitates the transfer of the powder from a scale pan or measure to a cartridge case.
Powder Measure - An adjustable volumetric measure that metres out uniform charges of powder. Used in the handloading of cartridges.
Powder Residue / Powder Ash - The deposit left in the bore, chamber and action of firearms after firing. If not cleaned out, will build up and cause inaccuracy in rifles and mechanical failure in semi-auto weapons and revolvers.
Powder Scale - A device used to weigh charges of powder. Normally of the balance beam type where markers, called "poise", are moved along a weight-graduated beam to the desired weight point. The scale pan is then filled until the balance point is reached.
Press - Mechanical device used in conjunction with dies for handloading ammunition.
Pressure - See Chamber pressure.
Primer - Small explosive metal cup in the head of a cartridge, containing fast-burning priming compound which, when ignited by friction ( by a blow from the firing pin ) provides the primary flash ( actually, a shock wave ) which ignites the main charge, thus converting the propellant powder into a gas. ( See Anvil, Berdan primer, Boxer primer, Flash hole and Ignition. )
Primer Blow-back - Primer in which gas pressure has blown out the section opposite the firing pin hole. May be due to weak main spring or to a firing pin that is too light.
Primer Indent - The dent or imprint made on the face of the primer by the firing pin. If cratered or pierced, it can indicate excessive pressures ( results of an overload ), or mechanical problems with the rifle.
Primer Leak - An escape of gas around the sides of the primer, usually the result of an overload. Evidenced by a dark circular smudge around the circumference of the primer in the case head. In severe cases the primer pocket will stretch so that the loosened primer falls out as the bolt is opened ( known as a "blown primer" ).
Primer Pocket - The recess in the base of the cartridge case that accepts the primer. In military ammunition, it is usually crimped and sealed with a lacquer sealant for water-proofing. ( Click here for picture. )
Primer Set-back - After firing primer is partly out of its seat.
Probability of Hit - Refers to the chance (denoted as a percentage) that a given round will hit the target at a given range. PoH values range from 0 to 100.
Progressive Powder - Slow-burning propellant that produces a more gradual pressure build-up.
Projectile - A bullet in flight. Often wrongly used to mean a bullet per se. A bullet does not become a projectile until it is in flight.
Proofing - The process of testing a firearm for strength by firing a cartridge in it that generates higher pressures than normal. If the firearm passes the test, it is deemed safe for use with normal loads. See Nitro proofing and Proof marks.
Proof Marks - Official symbols stamped onto the barrel of a firearm that has been proofed, to show that it is safe to use with standard ammunition appropriate to that firearm. Symbols differ from country to country. See Nitro proofing and Proofing.
Propellant - Another word for gun powder. See Powder.
Pump - A firearm action featuring a movable forearm which is manually actuated in motion parallel to the barrel. Forearm motion is transmitted to a breech bolt assembly which performs all the functions of the firing cycle assigned to it by the design. This type action is very prevalent in rimfire rifles and shotguns and to a lesser extent in centerfire rifles. Also called slide or trombone action. Usually associated with a tubular magazine.
Punctured primer - See Pierced primer.
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