This invention relates to a combination of a gun having a rifled barrel and a round of ammunition to be fired from said gun, and to a projectile for use in the combination, as described in
When a projectile is fired from a rifled barrel, the projectile must deform as it travels along the barrel so that material forming part of the projectile is forced into the spaces between the lands forming the rifling. This process is called engraving, and causes a spin to be imparted to the projectile by virtue of the longitudinal twist of the rifling.
The deformation of the projectile, its travel along the barrel effectively as a force fit to the rifling, the high linear acceleration imparted by the gun propellant on firing, and the consequent high rate of angular acceleration and associated force acting between rifling and projectile all contribute to substantial wear on the barrel.
If this wear rate can be reduced, substantial benefits follow, including increased barrel life, higher muzzle velocity and hence increased accuracy and lethality.
For this reason, low friction, readily deformable materials are normally selected for small arms bullets, for example lead. In order to increase the overall density of the bullet, it has also been proposed to use steel. However, steel is not readily deformable, and causes unacceptable barrel wear. On the other hand, hardness is a very desirable characteristic for the bullet material, in order to minimise nose tip ablation during penetration of hardened targets such as, for example, titanium/kevlar body armour. For these purposes, a Vickers Hardness of at least 550 (using a 10kg load) is the minimum desirable.
In seeking to overcome these problems, it has been common practice to make a small arms bullet from a steel core enclosed in a lead sheath which in turn is enclosed in a gilding metal jacket.
This latter solution is practical, but results in a bullet having a relatively expensive construction. This is a very significant disadvantage since small arms ammunition is consumed in large quantities, and the market for such ammunition is highly competitive.
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It would therefore be a considerable advantage if a way could be found to utilise steel or other metal having a Vickers Hardness equal to at least 550 (using a 10kg load) as the principal component of a small arms projectile, while enabling the projectile to be engraved by the rifling and not introducing unacceptable friction or wear, and avoiding the expensive construction of applying a jacket to the projectile.
According to the present invention there is provided a combination of a gun having a rifled barrel and a round of ammunition to be fired from said gun; the rifling of the barrel comprising rifling grooves which are separated by lands extending helically along a length of the barrel; the round of ammunition comprising a projectile; the projectile comprising: a body comprising a substantially cylindrical body portion comprising a plurality of splines or knurl lines producing a corresponding plurality of grooves which extend lengthwise along a section of the substantially cylindrical body portion; and a deformable jacket substantially surrounding the section of the substantially cylindrical body portion; wherein the body of the projectile is formed from a metal having a Vickers Hardness of not less than 550 HV, an outer diameter of said substantially cylindrical body portion is substantially equal to an internal diameter of the barrel defined by the land, an outer diameter of the deformable jacket is substantially equal to an internal diameter of the barrel defined by the rifling grooves, and wherein during firing of the projectile the deformable jacket is deformed by the lands of the barrel into the grooves formed between the splines or knurl lines of the projectile body.
The present invention also provides a projectile for use in the combination as claimed in claim 1; the projectile comprising: a body comprising a substantially cylindrical body portion comprising a plurality of longitudinally extending knurl lines or splines producing a corresponding plurality of grooves which extend lengthwise along a section of the substantially cylindrical body portion; and a deformable jacket substantially surrounding the section of the substantially cylindrical body portion;
Normally, the projectile will also have an ogival nose portion of the body forward of said substantially cylindrical body portion, although other forms are possible.
The body of the projectile (i.e. excluding the deformable jacket) should have a diameter which is not greater than that defined by the rifling lands. The deformable jacket of the projectile has an outer diameter which is designed so that upon firing of the projectile the rifling lands engage the deformable jacket which is designed to deform into the groove air gaps between said splines or knurl lines. The engagement of the deformable jacket with the rifling lands induces spin in the projectile due to the twist of the rifling. This deformation gives the projectile an interference fit with the rifling so as also to provide effective obturation by restricting or preventing the escape of propellant gases past the projectile via the rifling grooves. The length and precise diameter of the projectile should be designed with these factors in mind.
Regard must also be taken to ensure that the force required to effect the deformation of the jacket material and to propel the projectile along the barrel is not excessive, and this is the reason why the diameter of the body should not be greater than that of the rifling lands. This force is substantially reduced by the presence of the air gaps between the knurl lines or splines allowing the deformable jacket to deform into said groove air gaps during the passage of the body along the barrel.
The depth of said grooves in the projectile or knurl lines should preferably be between about 1% and 10% of the nominal calibre of the projectile, and an optimum design may be between 2% and 6%.
The material selected for the projectile body will depend partly upon the function which the projectile is to perform, but in the case of High Performance Ammunition should not be below a Vickers Hardness of 550 HV.
For a warshot ammunition nature to be used in combat conditions, steel is a suitable material, as it is inexpensive and can be readily formed into the desired shape, eg. by a cold-forming process. Tungsten is another possible material because hardness is an important characteristic for target defeat, as are alloys of tungsten, and tungsten carbide.
The invention is particularly but not exclusively applicable to small arms weapons systems, having a nominal calibre of 20mm or less, especially 9mm or less, such as 5.56mm.
The invention will now be described by way of example only with reference to the accompanying drawings, of which:-
As shown in Figure 1, a small arms ammunition projectile 1 comprises a body comprising a cylindrical body portion 2, a tip portion 3 and along the substantially cylindrical body portion a plurality of grooves or knurl lines 4 extending lengthwise along a section of the substantially cylindrical body producing a corresponding plurality of splines 5 and air gaps, or grooves, 6.
The projectile body is of elongate form and is cold formed from steel having a Vickers Hardness of at least 550. It can subsequently be given a heat treatment to provide the desired hardness or other physical properties.
Because of the substantial hardness of the projectile body material, the projectile is highly effective at penetration of targets such as titanium/kevlar body armour. Moreover, the hardness also serves to minimise ablation of the projectile tip profile, thus further contributing to its effectiveness in target penetration.
Figures 2A and 2B show representative cross sections A-A on Figure 1. In Figure 2A, the detail of the knurl lines 9 and associated 'groove' air gaps 6 of the projectile body 7 is shown when the projectile body 7 is located within a surrounding deformable jacket 11. Similarly, in Figure 2B, the splines 5 and associated 'groove' air gaps 8 of the projectile body 7 is shown when the projectile body 7 is located within a surrounding deformable jacket 11.
When the body 7 and deformable jacket 11 passes from the gun chamber into the rifled part of the barrel, by virtue of its diameter, the jacket material 11 is deformed by the lands of a rifled barrel into the corresponding groove air gaps 6, 8 corresponding to the splines 5 or knurl lines 9. The outer diameter 10 of the jacket material 11 should be substantially equal to the diameter of any rifling grooves (not shown).
The presence of the grooves 6, 8 facilitates the necessary deformation of the jacket 11, thus enabling the rifle engraving to take place with a substantially reduced axial force. The fact that the jacket material 11 can deform into the grooves 6, 8 contributes considerably to a dramatic reduction in the axial force required for engraving to occur.
Therefore, despite the hardness of the material forming the main part of the projectile body, barrel wear from this factor is minimised.
It will be evident to the skilled addressee that all of these factors reducing the engraving force will also result in reduced barrel wear, higher muzzle velocity, and hence increased lethality and accuracy.
The projectile which forms part of the combination of gun and ammunition according to the invention is also considerably less expensive to manufacture than a corresponding conventional projectile in, for example, a gilding metal jacket.
The optimum design parameters for the projectile according to the invention can be determined by those skilled in the art, based on the teaching contained herein.
The invention is particularly but not exclusively applicable to small arms ammunition. In one particular example, the invention has been successfully applied to 5.56mm gun and ammunition.
This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.