Rifling

Rifling is the term given to the spiral grooves cut into the bore of a barrel which impart a stabilizing spin to the bullet. This spin keeps the bullet travelling in a point-first direction and lessens any tendency for it to depart from its straight line of flight. As such, this was a very significant event in the evolution of firearms.

Some writers assign the invention of spiral-grooved barrels to Gaspard Kollner, a gunmaker of Vienna, in the fifteenth century. Others fix the date at 1520 and attribute it to Augustus Kotter of Nuremberg.

German weapons bearing the coat of arms of the Emperor Maximilian I and made between 1450 and 1500 have spiral-grooved barrels and are in fact the earliest identifiable rifled guns.

Both straight and spiral forms of rifling are encountered in early weapons, although it is generally accepted that the straight form of rifling was to accommodate the fouling produced in these early black powder weapons.

The number of grooves encountered can be anything from a single deeply cut rifling right up to 12 in number. The form of the groove also varies with square, round, triangular, ratchet and even comma shapes being encountered. The actual number of grooves appears to have little effect on the stabilizing effect of the rifling.

One of the problems encountered with the muzzle-loading rifle was the difficulty experienced in loading the projectile. If it was of sufficient diameter to take up the rifling, a large mallet was required to force it down the bore. If, on the other hand, it was of reduced diameter to assist in its insertion, the gases produced on firing would escape past the bullet leading to reduced velocity. In addition, the bullet took up little of the rifling and thus became unstable in flight. The Brunswick rifle overcame this problem by having a belted bullet and a barrel with two grooves to exactly match the rib on the bullet.

Several other designs were tried in which the bullet was rammed down onto various projections inside the breech end of the barrel. These projections deformed the bullet, thus filling out the bore. Unfortunately, the deformation was irregular and led to erratic behaviour of the bullet.

Greener in 1835 produced the first expansive bullet, the rear of which contained a steel plug. On firing, this was forced up into the bullet expanding it uniformly.

In 1852, Minie, a Frenchman, was awarded a British government contract for the production of an expanding bullet using a steel plug in the base very similar to the Greener design. This resulted in some acrimonious legal action by Mr Greener who was awarded a sum of money recognizing his as the earliest form of expanding bullet.

Lancaster, at about the same time as Minie invented his expanding bullet, produced a rifle with a spiral oval bore. This permitted easy loading of the bullet, did not require any mechanism to expand the base and, as there were no sharp corners to the rifling, it did not suffer the problems with fouling as encountered with conventional rifling.

In 1854, Whitworth patented the first polygonal bore rifling system which overcame most of the problems and was extremely accurate as well. Unfortunately, Whitworth did not have the experience in the practical manufacture of weapons and was unable to produce guns with the consistency required. As a result, his invention was soon overtaken by others.

Barrel land

Barrel groove

Figure 1.10 Rifling in the bore of a barrel.

The invention of the breech-loading weapon eliminated the problems of having to expand the bullet and fill the bore. The bullet could be made of the correct diameter and could simply be inserted into the rifling at the breech end of the barrel (Figure 1.10). In addition, instead of the deep grooving and a long soft bullet necessary for easy loading and expansion at the breech of a muzzle loader, shallow grooves and hard bullets could be used. This configuration resulted in more uniform bullets, higher velocities, better accuracy and improved trajectory.

1.1.12 Rifling twist rate calculation

One of the first persons to try to develop a formula for calculating the correct rate of twist for firearms was George Greenhill, a mathematics lecturer at Emmanual College in Cambridge, England.

His formula is based on the rule that the twist required in calibres equals 150 divided by the length of the bullet in calibres. This can be simplified to

where D = bullet diameter in inches and L = bullet length in inches.

This formula had limitations, but worked well up to and in the vicinity of about 1800 fps. For higher velocities, most ballistic experts suggest substituting 180 for 150 in the formula.

The Greenhill formula is simple and easy to apply and gives a useful approximation to the desired twist. It was based on a bullet with a specific gravity of 10.9, which is approximately correct for a jacketed lead-cored bullet.

In this equation, bullet weight does not directly enter into the equation. For a given calibre, the heavier the bullet, the longer it will be. So bullet weight affects bullet length, which is used in the formula.

For bullets with a specific gravity other than 10.9, then the formula becomes

Barrel land

Twist Rate

Barrel groove

Rifling Twist Rate Required = CD2/L xV SO/10.9

If an insufficient twist rate is used, the bullet will begin to yaw and then tumble; this is usually seen as 'keyholing', where bullets leave elongated holes in the target as they strike at an angle.

Once the bullet starts to yaw, any hope of accuracy is lost, as the bullet will begin to veer off in random directions as it processes.

A too-high rate of twist can also cause problems. The excessive twist can cause accelerated barrel wear, and in high -velocity bullets, an excessive twist can cause bullets to literally tear themselves apart under the centrifugal force.

A higher twist than needed can also cause more subtle problems with accuracy. Any inconsistency in the bullet, such as a void that causes an unequal distribution of mass, may be magnified by the spin.

Undersized bullets also have problems, as they may not enter the rifling exactly concentric and coaxial to the bore, and excess twist will exacerbate the accuracy problems this causes.

The twist necessary to stabilize various calibres follows (Table 1.1):

Table 1.1 Rifling twist necessary to stabilize various calibres.

Calibre Twist rate required

Table 1.1 Rifling twist necessary to stabilize various calibres.

Calibre Twist rate required

0.22 Short

1 in

24"

0.22 Long rifle

1 in

16"

0.223 Remington

1 in

12"

0.22-250 Remington

1 in

14"

0.243 Winchester

1 in

10"

6 mm Remington

1 in

9"

0.25-0.6 Remington

1 in

10"

0.257 Weatherby Magnum

1 in

10"

6.5 x 55 Swedish Mauser

1 in

7.5"

0.260 Remington

1 in

9"

0.270 Winchester

1 in

10"

7 mm-0.8 Remington

1 in

9.25"

7 mm Remington Magnum

1 in

9.25"

0.30 Carbine

1 in

16"

0.30-30 Winchester

1 in

12"

0.308 Winchester

1 in

12"

0.30-0.6 Springfield

1 in

10"

0.300 Winchester Magnum

1 in

10"

0.303 British

1 in

10"

0.357 Magnum

1 in

16"

0.357 Sig Saner

1 in

16"

0.380 Automatic Colt Pistol

1 in

10"

9 mm Parabellum

1 in

10"

0.40 Smith & Wesson

1 in

15"

0.45 Automatic Colt Pistol

1 in

16"

0.444 Marlin

1 in

38"

0.45-70 Government (US)

1 in

20"

Whilst it is of little circumstance, the question as to the revolutions made per minute by the bullet has been asked on several occasions. The formula for calculating this is as follows:

Twist rate in inches

For example:

9 mm PB bullet at 1200 fps fired in a barrel with a 1 in 10 twist rate will have a rotational speed of 1200 x 720/10 = 86 400 rpm 0.223" bullet at 3000 fps fired in a barrel with a 1 in 12 twist rate will have a rotational speed of 3000 x 720/12 = 180 000 rpm

Once again, whilst it has little relevance in everyday case examination, the question as to the rotational speed (revolutions per minute, rpm) and the number of times that a bullet will make a full rotation whilst passing through an object can be asked.

This question was posed in relation to a murder case where one of several bullets which had hit the deceased had cut a trough (often called a 'gutter wound') across the victim 's arm. The bullet wound was black and the defence counsel were of the opinion that this was caused ' by the bullet rotating so fast that it had burnt the flesh to carbon'.

This was extremely easy to refute as the barrel of the weapon concerned had a 1 in 10" rate of twist, which means that the bullet rotated once in every 10 in. of travel. As the wound on the arm was barely 2 in. in length, the bullet would not have made more than j of a rotation during that distance.

The blackening, as can be seen from the following photograph, was simply old congealed blood (Figure 1.11).

Deane Adams Firearm
Figure 1.11 Gutter wound to forearm.

1.1.13 The revolver

A revolver is a weapon with a revolving cylinder containing a number of firing chambers (basically a revolving magazine) which may be successively lined up and discharged through a single barrel.

In the long history of revolvers, no name stands out more strongly than that of Samuel Colt. But as we have seen earlier, Colt did not, despite his claims to the contrary, invent the revolver.

The earliest forms of the revolver include a snaphaunce revolver made in the days of King Charles I, said to have been made before 1650 and an even earlier weapon made during the reign of Henry VIII some time before 1547.

Those early revolvers were, surprisingly enough, practically identical to the actions covered in Colt' s early patents. The actions for those early patents are still in use today in the Colt Single Action Army or Frontier model.

Colt's original patent, dated 1835, dealt with the revolving of the cylinder by a ratchet and pawl arrangement. The original patents belonging to Colt were so tightly worded that no other manufacturer had any real impression on the market until the original patents ran out in 1850. After this the market was open with Dean-Adams in 1851, Beaumont in 1855, and Starr and Savage in 1865, all bringing out innovative designs. These were, however, still all muzzle-loading percussion systems.

It was not until the advent of the rimfire, which was introduced at the Great Exhibition in 1851, that breech - loading revolvers really started. Even then, it was not until 1857 that Smith and Wesson introduced the first hinged-frame 0.22" rimfire revolver. The patent for bored-through chambers and the use of metallic cartridges gave Smith and Wesson the market until 1869.

With the passing of the Smith and Wesson patents, there was a flood of breech-loading arms in calibres from 0.22 to 0.50- . The day of the rimfire, except for 0.22" target shooting, was, however, numbered by the introduction of the centre fire (Figure 1.12).

The first centre fire Colt revolver to be patented was the Colt Single Action Army Model 1873. In 1880, Enfield produced a 0.476" hinged-frame revolver, but it was a design monstrosity and was soon superseded by the now familiar Webley top latching hinged-frame design in 1887. In 1894, it was slightly modified and became the standard Webley Mk 1 British Army service revolver. In 1889, the US government officially adopted a Colt 0.38" revolver using the now familiar swing-out cylinder system.

A multitude of variations on the Smith and Wesson and Colt designs followed, but little has really changed in the basic design of the revolver mechanism since then, apart from improved sights, better metals allowing higher pressures and different grips. It would seem, however, that little can be done to improve on the efficiency of the basic Smith and Wesson and Colt designs.

Revolver Long Barrel
Figure 1.12 Revolver.

1.1.14 Self-loading pistols

The principle of the self-loading pistol was grasped long ago, but without the necessary combination of a self-contained cartridge, smokeless propellant and metallurgical advances, it was not possible to utilize the principles involved.

It is reported in Birche's History of the Royal Society for 1664 that a mechanic had made a claim of being able to make a pistol which could 'shoot as fast as presented and stopped at will ' .

Whilst patent records from 1863 show numerous attempts to develop a self-loading pistol, it was not until 1892 that the first successful weapon appeared. This was a weapon patented by the Austrian Schonberger and made by the company Steyr. It was a blowback design and was made for the 8 mm Schon-berger, a very powerful cartridge.

The first commercially successful design was by an American, Hugo Bor-chardt. Unable to finance his design, he took it to Germany to have it manufactured there. This weapon, although clumsy, was of radical design containing the first magazine to be held in the grip and the 'knee joint ' toggle locking system. It was this design which was slightly modified by Luger to become Germany's first military self-loading pistol.

In 1893, Bergman produced a whole range of pistols, one of which, the 1897 8 mm 'Simplex', is of particular interest as the cartridge became the 0.32" Automatic Colt Pistol (ACP) cartridge.

Revolver Long Barrel

Magazine

Figure 1.13 Self-loading pistol.

Magazine

Figure 1.13 Self-loading pistol.

In 1896, the story of the truly successful self-loading pistol really began with the introduction of the 7.63 mm calibre Mauser, the 'broom handle' pistol. This was the pistol made famous by Winston Churchill who purchased one for use during the Sudan campaign of 1898. Winston Churchill credits the weapon with saving his life when he shot his way out of a native trap 'killing several Fuzzy Wuzzies'!

In 1898, the German factory of DWM (Deutsche Waffen- and Munitionsfabriken Atkien-Gesellschaft, German Weapons and Munitions Works) brought out the first model of the famous Luger pistol in 7.65 mm Parabellum calibre. In 1904, the weapon was made available in 9 mm Parabellum, which was the calibre adopted for the German service pistols.

In 1897, John Browning, the greatest of all American small arms designers, produced his first patent. This was finally introduced as the Model 1900 Colt 0.38" automatic.

Webley made a few unsuccessful forays into the self- loading pistol market with the 0.455" calibre 1904 model, the 0.45" 1905 model, the 1910 0.38" calibre and the 0.455" navy model 1913. The Webley design was not, however, very successful and never became popular.

Probably the most successful pistol ever to be introduced was the Model 1911, Browning designed, Colt Government Model in 0.45" calibre. With minor modifications, as the Model 1911 Al, the weapon was the standard issue military weapon for the United States until the late 1980s.

Since then, the main innovations have been in the use of lightweight aluminium and plastics for the weapons frame, the move towards smaller calibres and higher-velocity bullets, the development of magnum handgun ammunition and the use of gas-operated locking systems. These are, however, only variations on a theme and, as with revolvers, it would seem that there is little that can be done to improve on the basic design.

1.1.15 Brief glossary

Breech loader

Centre fire

Flash hole

Flash pan

Mercury fulminate Muzzle loader

Pinfire

Primer cap Priming powder Propellant

Revolver

Rifling

Rimfire

Self-loading

Weapon in which the ammunition is inserted into the rear of the barrel.

Ammunition with the priming compound held in a cap in the centre of the base of the cartridge case.

The spring-loaded hammer system which initiates the priming compound.

The vice- like component of a flintlock mechanism which holds the flint.

Hole connecting the priming compound with the propel-lant charge; also called the vent or touch hole.

Shallow pan covering the touch hole into which the priming powder is placed.

One of the earliest explosive priming compounds.

Weapon in which the propellant and ball are loaded from the muzzle.

Early self-contained cartridge which had a firing pin integral with the cartridge case. Small cup containing the priming compound. Finely divided black powder.

Solid substance which, when ignited, produces a large quantity of gas to propel a missile down the bore of a weapon.

A weapon with a revolving cylinder containing a number of firing chambers (basically a revolving magazine) which may be successively lined up and discharged through a single barrel.

Spiral grooves in the barrel to impart spin to the projectile giving it stability in flight.

Self-contained cartridge with the priming compound held in the hollow base flange or rim.

A repeating firearm requiring a separate pull of the trigger for each shot fired. After manually loading the first round from the magazine, the weapon will use the energy of discharge to eject the fired cartridge and load a new cartridge from the magazine into the barrel ready for firing.

+1 0

Responses

  • LEILA
    How to calculate the spiral angle when twist rate of gun is given?
    8 years ago
  • beverly
    Who had the first patent on rifling?
    8 years ago
  • isto
    How to improve the percussion on a smith wesson revolver screw?
    7 years ago
  • gormadoc
    What are riflings ballistic?
    2 years ago
  • euan king
    What is the rate of twist on a lancaster oval barrel gun?
    7 months ago

Post a comment