Lands And Grooves Ballistics

and those portions of the bore which are situated between the grooves are known as lands.

Gauge or Calibre-—Both types of firearms are classified by the Gauge, or Calibre, of their bores; that is by the internal dimension of the barrel A different system of measuring, however, exists for large smooth-bores and rifled arms.

Large smooth-bores are measured by the number of

M16 Barrel Rifling Pictures
Pig. x.—Cross-section of a rifled barrel showing the grooves and lands.

spherical balls of pure lead, each exactly fitting the inside of the bore, which go to make up a pound. For example, a 12-bore (or 12-gauge) is a weapon in which the bore is of such a size that twelve spherical lead bullets, each exactly fitting the bore, will together weigh one pound.

This method of indicating the size of the bore is very old and dates back to the days of muzzle-loading cannon. A cannon which fired a solid round shot of twelve pounds was described as a "Twelve Pounder," and so on for other sizes. Similarly smooth-bore muskets and guns were known by the weights of the bullets which they

Forensic BallisticsForensic BallisticsForensic Ballistics

(A) A High-grade double-barrelled hammerless Sporting Gun open ready for loading The arrow indicates the extractors

(B) Three fired -22 rim-fire cartridge cases, each fired by a different rifle

(C) Three more fired -22 rim-fire cartridge cases, each fired by a different rifle The difference in the shapes, sizes and positions of these six different striker indentations is obvious fired. Such bullets were of lead and spherical in shape. Their weights were sometimes given in ounces, but more often by the number of bullets which went to the pound. For example, a 2-ounce spherical bullet of solid lead was a No. 8, since eight such bullets made up a pound; a i-ounce spherical lead bullet was a No. 16, because sixteen such bullets weighed a pound; and so on.

Nowadays a No. 8, or a No. 16 would be termed an 8-gauge (or 8-bore), or a 16-gauge (or 16-bore).

In Great Britain the size of the gauge or bore is actually measured at a point 9 inches from the breech, as laid down by the Proof Act and Rules.

In rifled arms the size is denoted by the actual diameter of the bore across the lands, that is by the smallest possible diameter of the bore (see Fig. 1).

In Great Britain and America this measurement (known as the calibre) is given in decimals of an inch, e.g. -250, •303, '455, etc. But on the Continent it is given in millimetres, e.g. 6*35, 6*5, 7*9, 8, 9*3, etc.

There are two exceptions to both these general systems of measurement.

Smooth-bores of a smaller gauge than No. 32 are denoted by the diameter in decimals of an inch, e.g. *4io, ♦360; and this applies generally if the bore is less than 0*5 inch.

Rifled arms of larger calibre than *6oo are usually classified according to their gauges, e.g. io-bore, 8-bore, etc.

Parts of the Barrel.—The inside of the barrel of any arm consists of three parts.

The first of these is the chamber which is the portion at the breech end which accommodates the cartridge, and which is made to a shape which fits the particular type of cartridge which is used in the individual arm.

The chamber is almost always of considerably larger diameter than the actual bore, and is consequently connected to the bore by a taper.

In rifled arms this taper is known as the Lead, or Leed. The former spelling is more pedantically correct, as it denotes that portion of the inside of the barrel which leads from the chamber to the bore. But since the metal lead plays such a big part in shot and bullets, there is liable to be confusion of meaning if the same spelling is used for two such different things. For this reason the phonetic spelling, Leed, has come largely into use and will be adopted throughout this book.

The Leed is usually very short, that is less than half an inch in length.

In smooth-bores this connecting taper is called the chamber cone. In British guns the chamber cone is usually from § to I inch in length, but in some Continental guns this cone may be as long as 2 inches.

The bore is that part of the inside of the barrel which lies between the front end of the Leed, or Chamber Cone, and the muzzle.

In a rifled arm this is the portion which is grooved, or rifled; and it is, or should be, perfecdy cylindrical.

In a smooth-bore portions of the bore may be enlarged slightly after Proof in order to improve the shooting qualities of the weapon, and it is for this reason that the Proof Act fixes a point 9 inches from the breech for the purpose of measuring the gauge.

In the case of smooth-bore weapons with barrels shorter than 9 inches the gauge is, of course, as measured.

Breech Face,—The breech end of the chamber is sealed by a solid flat block of metal against which the barrel comes into position when the weapon is closed for firing, and which is termed the breech face.

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Responses

  • savannah
    How to open the barrel groove?
    5 years ago
  • daniele
    Is bore measured lands or grooves?
    4 years ago
  • Learco
    What are lands ballistics science?
    4 years ago
  • tom
    What is grooves and lands in the balistic?
    2 years ago
  • arabella
    What is grooves in ballistics?
    2 months ago

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