GB2269654A

GB2269654A - A method of preventing the buildup of deposits of plastics material in a chokedand rifled barrel of an air,gas or spring gun.

Info

Publication number: GB2269654A
Application number: GB9216961A
Authority: GB
Inventors: Hugh Edward Earl
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-08-11
Filing date: 1992-08-11
Publication date: 1994-02-16
Anticipated expiration: 2012-08-11
Also published as: GB9216961D0; DE4326878A1; GB2269654B

Abstract

A pellet for use in the method has a metal head portion (1) and plastics tail portion (2). Maximum diameter portions (21, 22) on the tail portion (2) ensure that the pellet has low frictional losses as it passes along the bore of the gun barrel. Because the gun barrel bore has a choke, i.e. it tapers at its muzzle end, some of the tail portion (2) will be turned into swarf by the choke and will become stuck in the rifling. The head portion (1) has a metal maximum diameter portion (11) in order to clear from the rifling in the choke any swarf left by the previous pellet, without generating unwanted frictional losses in the unchoked part of the bore by imparting spin to the pellet by projecting into the rifling. <IMAGE>

Description

2269654 A METHOD OF PREVENTING THE BUILDUP OF DEPOSITS OF PLASTICS

MATERIAL IN A CHOKED AND RIFLED BARREL OF AN AIR, GAS OR SPRING GUN The present invention relates to a method of preventing the buildup of deposits of plastics material in a barrel of an air, gas or spring gun having a choked and rifled bore.

In my U.K. patent No. 2,023,779, 1 describe a pellet having a metal head portion, a plastics tail portion and two maximum diameter portions on the tail portion which seal against the bore of the gun barrel. The plastics tail portion ensures that there are low frictional losses as the pellet passes along the bore and that the bore is not scratched or otherwise subjected to excessive wear. The reader is referred back to my earlier U. K. patent for a complete description of the pellet that it discloses. At the time that I invented my earlier pellet at the end of the 1970s, barrel bores for air, gas or spring guns did not generally have any choke, i.e. tapering at the muzzle end of the bore. Choked bores were generally found only on shotguns. The pellet disclosed in my earlier U.K. patent was intended to be an improvement on the conventional lead pellet. Such conventional lead pellets have continued to be used and, in order to attempt to improve the accuracy of conventional lead pellets, many air gun manufacturers have now started to produce guns which have bores that are choked at their muzzle end. Whilst this sumetimes improves the accuracy of conventional lead pellets, the choking adjacent to the muzzle end of the bore causes problems for the pellet of my earlier U.K. patent. This is because the choke strips fine threads from the plastics tail portion of each pellet as it passes along the bare.

The wisps or swarf from successive pellets builds up in the rifling of the bore and causes what is otherwise a very accurate pellet to become inaccurate.

U.K. Patent Specification No. 2,029,940 discloses a dart f or an air gun. The dart has a plastics cylindrical central portion and a plastics finned tail portion. The head portion is made of metal and has a narrow tip which projects forwards from a shoulder portion. The metal shoulder portion forms a smooth continuation of a plastics boss at the front of the central portion. The metal head portion has a maximum diameter (at its shoulder portion) which is less than 3/4 of the maximum diameter of the plastics central and tail portions. For this reason, the metal head portion does not touch the bore of the gun barrel. Thus, the metal head portion, which is made of steel and is therefore harder than the material of the barrel, does not scrape or otherwise damage the barrel bore.

There is currently sold a modification of the above dart which is illustrated in U.K. Patent Specification No. 2,099,962. In the modified version the four rearwardly projecting, semicircular flaps at the rear end of the plastics central portion are angled slightly outwards in order to form a maximum diameter portion at the rear of the central portion. The shoulder portion of the metal head portion has substantially the same diameter as the plastics central portion and is longer than in GB-A-2,029, 940. Also, the boss at the front of the central portion is not present and the shoulder portion of the head portion forms a substantially smooth continuation of the central portion. There is a very slight maximum diameter portion at the front of the metal shoulder portion but it has a smaller diameter than the rear maximum diameter portion defined by the four flaps.

All darts are usually shot down bores which are not rifled. This is because the dart has its tail fins and therefore does not need to be spun by rifling in order to be gyroscopically stabilized.

When the dart of GB-A-2,099,962 is shot down a bore of appropriate calibre, the plastics rear maximum diameter portion locates the dart in the centre of the bore but the diameter of the steel front maximum diameter portion is less than the diameter of the bore (if the bore is not rifled) or the inner diameter of the rifling in the bore (if the bore is rifled). This is the case even if the bore is choked towards its muzzle. Because of the limited diameter of the front maximum diameter portion, the steel head portion does not score the bore and the front of the dart is free to rattle along the bore, giving poor yaw control. In particular, it should be noted that, if the bore is rifled, the steel front maximum diameter portion does not enter the rifling. Again, if the bore is rifled, the plastics rear maximum diameter portion must form a seal with the rifling in order to contain the propelling gases. Under such circumstances, wisps will be stripped off the plastics rear maximum diameter portion as the dart moves along the bore and the wisps will build up in the rifling.

U.K. Patent Specification No. 1,114,608 discloses in Figure 2 a shotgun bullet which may be fired out of a choked barrel. As shotgun barrels are not rifled, the bullet has a front maximum diameter portion which is made of metal and incorporates air passages which impart spin to the bullet once it has left the barrel. A plastics rear maximum diameter portion seals against the barrel bore. The absence of rifling means that wisps are not stripped off the plastics rear maximum diameter portion.

U.K. Patent Specification No. 2,170,301 discloses a bullet for a large calibre handgun. The bullet has two metal front maximum diameter portions which project into the rifling of the handgun to impart spin to the bullet. A plastics rear maximum diameter portion seals against the rifling. Because the barrel of the handgun is not choked, there is no stripping of plastic off the rear seal. Because the two metal front maximum diameter portions project into the rifling along the full length of the barrel bore, there are frictional losses. These are not significant in a handgun, but they would be significant in an air, gas or spring gun that has available considerably less propulsive energy.

According to the present invention, there is provided a method of Dreventing the buildup of deposits of plastics material in a barrel of an air, gas or spring gun having a bore which is choked only adjacent to its muzzle and which has rifling that 4 def ines inner and outer bore diameters, the method comprising loading into the gun and shooting along and out of the bore a pellet which is elongate along a central axis and comprises: a first body portion made of metal or metal containing plastics material; a second body portion made of plastics material; and first and second axially spaced maximum diameter portions; wherein the first maximum diameter portion is provided by the second body portion and imparts spin to the pellet by projecting into the rifling as the pellet passes along the unchoked and choked parts of the bore, and the second maximum diameter portion (i) is made of metal or metal containing plastics material, (ii) projects into the rifling of the choked part of the bore and (iii) does not impart spin to the pellet by projecting into the rifling as the pellet passes along the unchaked part of the bore.

If previous pellets have left wisps of plastics material in the rifling of the choked part of the bore, the second maximum diameter portion, because it is made of metal or metal containing plastics material and because it projects into the rifling of the choked part of the bore, will entirely remove the wisps or remove sufficient of them to prevent them from building up to a level at which they would significantly affect the accuracy of pellets shot by the gun. Thus the method of the present invention ensures that the pellet, when used in a choked and rifled bore, is as accurate as a pellet according to my earlier U.K. patent No. 2,023, 779, when used in a parallel and rifled bore. The pellet of the present invention may of course be used in a parallel bore and will be as accurate as the pellet of my earlier patent when used in such a parallel bore, but if this is done there will be no wisps for the second maximum diameter portion to scrape out.

It is only the choked part of the bore that is prone to strip plastics material off the first maximum diameter portion. Thus, only the choked part requires cleaning. The unchoked part does not require cleaning. The present invention makes use of this fact to reduce the frictional losses. This is achieved by using 'the plastics first maximum diameter portion, and not the metal or metal containing plastics second maximum diameter portion, to impart spin to the pellet by projecting into the rifling of the unchoked part of the bore.

The diameter of the second maximum diameter portion may be the same as the inner bore diameter of the unchoked part of the bore, but, in most practical embodiments, the diameter of the second maximum diameter portion is less than the inner bore diameter of the unchoked part of the bore, and therefore also less than the diameter of the first maximum diameter portion. Also, the material of the second maximum diameter portion is softer than the material of the gun barrel bore, in addition to being harder than the material of the first maximum diameter portion.

Preferably, the pellet has only the two maximum diameter portions in order to minimize frictional losses.

If the first maximum diameter portion forms an air-tight seal against the bore along its full length in order to contain the air or gas, it is preferable that the diameter of the first maximum diameter portion is greater than the largest outer bore diameter, i.e. the outer bore diameter of the unchoked part of the bore.

If the diameter of the second maximum diameter portion is the same as or just slightly less than the inner bore diameter of the unchoked part of the bore, then the second maximum diameter portion helps guide the pellet (keep it centrally aligned) along the full length of the bore.

-6 Many arrangements of the pellet are possible. For example, the first body portion may be a tall portion and the second body portion may be a head portion, or vice versa. In a further alternative, the first body portion is a head and tall portion and the second body portion is located around the head and tall portion intermediate the ends thereof.

The second maximum diameter portion may be behind or in front of the first maximum diameter portion, with the precise location depending on the design of the pellet.

The second maximum diameter portion may be provided by the first body (e. g. head) portion for ease of manufacturing. Alternatively, it may be provided by a disc- or ring-like member located between the first and second (e.g. head and tall) portions.

Preferably, the pellet further comprises a third maximum diameter portion which is axially located between the first and second maximum diameter portions. If the third maximum diameter portion is provided by the head portion, this results in a pellet having a comparatively long head portion and therefore a comparatively high weight (ballistic coefficient) with associated good range and good energy retention at long ranges. If the third maximum diameter portion is provided by the tall portion, the third maximum diameter portion may be considered to be functionally redundant but it does enable the use of a tail portion of the type shown in my earlier U.K. patent No.,2,023,779. This commonality of tall portions between my old and new inventions leads to manufacturing efficiencies.

The second maximum diameter portion may have an annular forwardly- facing face which is substantially perpendicular to the central axis and an annular radially outwardly-facing face which is substantially cylindrical. The edge where the forwardly-facing face joins the radially outwardlyfacing face provides a scraping edge which is effective at scraping out plastics material deposited in the rifling. The forwardly -facing face, instead of being substantially perpendicular to the central axis, may face outwards and form an acute angle (e.g. greater 7 than 40', 500, 600, 70 or 80 with the central axis. If a third maximum diameter portion is provided by the head portion, then the first maximum diameter portion should have a bigger diameter than both the second and third maximum diameter portions.

Preferably, the second body portion has, at least adjacent to the first maximum diameter portion, a part whose diameter is substantially the same as the inner bore diameter of the unchoked part of the bore. This part helps centre the pellet in the bore. The part may be an intermediate diameter portion adjacent to the first maximum diameter portion and axially located between the first and second maximum diameter portions.

The invention will now be described by way of non-limiting embodiments with reference to the accompanying drawings, in which:- Pigs. la and 1b are side and front end views respectively of a first embodiment of a pellet for use in the method of the present invention; Figs. 2a and 2b are side and front end views respectively of a second embodiment of a pellet for use in the method of the present invention; Figs. 3a and 3b are side and front end views respectively of a third embodiment of a pellet for use in the method of the present invention; and Figs. 4a and 4b are side and front end views rtspectively of a fourth embodiment of a pellet for use in the method of the present invention.

Referring to the first embodiment of Figs. la and lb, the pellet comprises a head portion 1 and a tail portion 2. The head portion 1 is made of any convenient metal such as lead, brass or an alloy of lead, copper and tin, bismuth or zinc, or of metal containing plastics material, such as PTFE, nylon or polyethylene containing a metal filler or loading such as powdered bronze and/or zinc. For all four embodiments, the material of the head 8 portion 1 is harder than the material of the tail portion 2, but softer than the material of the gun barrel bore.

Whilst the head portion 1 is shown in the Figures as having a pointed tip, it may have a different tip shape or no tip at all, e.g. a flat front face for paper target shooting.

The tail portion 2 is made of plastics material, with a low coefficient of friction and sufficient elasticity to regain its shape after deformation, such as PTFE, nylon or polyethylene.

The head 1 has a maximum diameter portion 11. The tail portion 2 has two maximum diameter portions 21 and 22. All three maximum diameter portions 11, 21 and 22 are axially spaced along the centre line CL of the pellet.

The maximum diameter portion 11 comprises a forwardlyfacing annular face 12, a radially outwardly- facing annular face 13 and a rearwardly-facing annular face 14. The two faces 12, 14 are perpendicular to the centre line CL and the face 11 is substantially cylindrical with respect to the centre line CL. However, the faces 12, 14 may face partially outwards as well as forwards or backwards. In front of the face 12 is a radially outwardlyfacing annular face 15 which is cylindrical with respect to the centre line CL. The face 15 is produced by machining in order to create the face 12. Extending rearwardly from the face 14 along the centre line CL is a-rod 16.

The tail portion 2 has a through bore 23 which extends along the centre line CL, a convexly curved annular surface 24 between the two maximum diameter portions 21 and 22 and a reduced diameter boss 25 in front of the maximum diameter portion 21. The bore 23 may be blind at its rear end and the annular surface 24 may be cylindrical and not convexly curved.

In order to secure the head and tail portions 1, 2 together, the rear end 17 of the rod 16 of the head portion 1 is deformed in order to engage the bore 23 of the tail portion 2.

9 Preferably, however, the rod 16 is a force or friction fit in the bore 23, for ease of manufacturing.

It should be noted that in Figure la, and also in Figures 2a, 3a and 4a, the separate components are shown with exaggerated axial spacing gaps between them in order to aid understanding of the drawings.

Figure lb is a front end view of the first embodiment. As may be seen, the maximum diameter portions 21, 22 have circular profiles and are just visible behind the circular profile of the maximum diameter portion 11. The radial extent of maximum diameter portions 21, 22 that is visible has been exaggerated for the sake of clarity. The two maximum diameter portions 21, 22 have approximately the same diameter, which is slightly bigger than the diameter of the maximum diameter portion 11. For a pellet for a nominal 5.5 mm bore, examples of diameters are as follows: maximum diameter portion 22 (5.7 mm), maximum diameter portion 21 (5.5 mm) and maximum diameter portion 11 (5.45 mm).

The relative dimensions of maximum diameter portions 11, 21, 22 achieve the following effects. The maximum diameter portions 21, 22 project into the rifling of the unchoked and choked parts of the bore (e.g. a nominal 5.5 mm bore) of the gun barrel and thereby spin the pellet. Because of the low friction of the material of the tail portion 2, they also ensure that the pellet progresses along the barrel with low frictional losses. The slightly smaller diameter of the maximum diameter portion 11 ensures that it acts only in the choked part of the bore in order to scrape away any swarf left in the rifling of the choked part by the tail portion 2 of the previous pellet. The scraping action is achieved by a cutting or scraping edge formed at the annular junction between the faces 11, 12. The-rearmost maximum diameter portion 22 seals against the gun barrel bore in order to prevent leakage past the pellet of the compressed air or the like which is propelling the pellet along the barrel. As explained serves to scrape away previously, the maximum diameter portion 11 swarf left by previous pellets. The maximum diameter portion 21 is not essential and may be dispensed with. It is shown as being present in the f irst embodiment in order that the present invention may use the same tail portion 2 as my previous invention described in U.K. patent No. 2, 023,779.

Regarding the second embodiment shown in Figures 2a and 2b, many aspects are the same as for the f irst embodiment and the same reference numerals have been used where appropriate. The head portion 1 is different in that it has a cylindrical portion 18 behind the maximum diameter portion 11. A maximum diameter portion 19 is provided at the rear of the cylindrical portion 18. A blind bore 110 is located in the rear of the head portion 1 and passes through the maximum diameter portion 19 and into the cylindrical portion 18. The blind bore 110 is located along the centre line Cl.

The tail portion 3 of the second embodiment is much shorter than the tail portion 2 of the first embodiment. The tail portion 3 comprises essentially only a maximum diameter portion 31 in the shape of a disc and a forwardly projecting rod 32 that is force fitted into the blind bore 110 in order to hold together the head and tail portions 1, 3. As with the-first embodiment, the maximum diameter portion 31 has a circular profile with a diameter slightly greater than that of the circular profiles of the maximum diameter portions 11, 19 of the head portion 1. The maximum diameter portion 31 acts as a seal for sealing in the compressed air that propels the pellet and the maximum diameter portions 11, 19 of the head portion 1 scrape away any swarf left in the rifling of the choked part of the bore by previous pellets. The maximum diameter portion 11 or 19 is not essential and may if desired be dispensed with, leaving the other maximum diameter portion of the head portion 1 to scrape away the swarf by itself. Because a large percentage of the second: embodiment is metal, the pellet has a high ballistic coefficient which gives a good range and energy retention at long ranges.

The third embodiment of Figures 3a and 3b is very similar to the first embodiment except that the head portion 1 does not have a maximum diameter portion 11. Instead, the maximum diameter portion 41 is provided separately by an annular metal spacer 4 having faces 42, 43, 44 analogous to the faces 12, 13, 14 of the maximum diameter portion 11 of the first embodiment. The rod 16 passes through a hole 45 in the spacer 4 in order to connect to the main part of the head portion 1.

The tail portion 2 is shown as not having the boss 25 of the first embodiment but this may be provided if desired. Preferably, the dimensions of the spacer 4 are the same as those of the maximum diameter portion 11 of the first embodiment, with the dimensions of the maximum diameter portions 21, 22 of the tail portion 2 being the same as those of the first embodiment.

The fourth embodiment of Figures 4a and 4b is very similar to the first embodiment. The head portion 1 differs in that the rod 16 is of greater diameter and projects rearwardly from a boss 111 that is located axially behind the maximum diameter portion 11. The rod 16 is received within a blind bore 29 of the tail portion 2. There is also a separate, second blind bore 26 of the tail portion 2.

In addition to the maximum diameter portion 22, the tail portion 2 also has an intermediate diameter portion 27 immediately in front of the maximum diameter portion 22. The rest of the radially outermost surface of the tail portion 2 forms a minimum diameter portion 28. Thus, the diameter of the tail portion 2 increases by a series of steps in the rearward direction.

The maximum diameter portion 11 and the intermediate diameter portion 27 have diameters which are slightly less than (substantially the same as but not greater than) the inner bore diameter of the unchoked part of the bore. This ensures that these two portions form a sliding fit with the unchoked part of the bore and thereby centre the pellet as it passes along the unchoked part of the bore. The maximum diameter portion 22 acts as a seal. The boss 111 and the minimum diameter portion 28 have a common diameter which is less than the inner bore diameter of the choked part of the bore. Thus, the boss 111 and minimum diameter portion 28 do not cause frictional losses.

The maximum diameter portion 22 projects into the rifling of both the unchoked and choked parts of the bore, thereby imparting spin to the pellet along the full length of the bore. The metal maximum diameter portion 11 only starts to project into the rifling when the pellet passes from the unchoked part to the choked part of the bore. It is at this stage that the maximum diameter portion 11 starts to effect its function of scraping out any plastics material previously deposited in the choked part of the bore. Because the maximum diameter portion 22 has already spun the pellet up to speed, the maximum diameter portion 11 does not, in the choked part of the bore, make any significant contribution to spinning the pellet.

For a nominal 5.5 mm bore, a suggested diameter for the maximum diameter portion 22 is 5.8 mm. The suggested diameter for the intermediate diameter portion 27 and the maximum diameter portion 11 is 5.45 mm. The suggested diameter for the minimum diameter portion 28 is 5.15 mm. The suggested axial thickness d for the maximum diameter portion 11 ranges from 0.22 to 0.25 mm, depending on whether the head portion 1 is made for example from zinc or copper.

The bore diameters for the nominal 5.5 mm bore are: in the unchoked part of the bore, an inner bore diameter of 5.47mm and an outer bore diameter of 5.59 mm; and, in the choked part of bore, at the muzzle, an inner bore diameter of 5.42 mm and an outer bore diameter of 5.56 mm. It may therefore be seen that the diameter of the maximum diameter portion 11 is less than the inner bore diameter of the parallel, unchoked part of the bore, and is greater than the inner bore diameter but less than the outer bore diameter of the muzzle end of the choked part of the bore. Typically, the unchoked part of the bore is at least ten times as long as the choked part of the bore.

14

Claims

1. A method of preventing the buildup of deposits of plastics material in a barrel of an air, gas or spring gun having a bore which is choked only adjacent to its muzzle and which has rifling that defines inner and outer bore diameters, the method comprising loading into the gun and shooting along and out of the bore a pellet which is elongate along a central axis and comprises:

a first body portion made of metal or metal containing plastics material; a second body portion made of plastics material; and first and second axially spaced maximum diameter portions; wherein the first maximum diameter portion is provided by the second body portion and imparts spin to the pellet by projecting into the rifling as the pellet passes along the unchoked and choked parts of the bore, and the second maximum diameter portion (i) is made of metal or metal containing plastics material, (ii) projects into the rifling of the choked part of the bore and (iii) does not impart spin to the pellet by projecting into the rifling as the pellet passes along the unchoked part of the bore.

2. A method according to claim I. wherein the diameter of the second maximum diameter portion is less than the inner bore diameter of the unchoked part of the bore.

3. A method according to claim 1 or 2, wherein the f irst maximum diameter portion forms an air-tight seal against the unchoked and choked parts of the bore of the gun.

4. A method according to any one of claims 1 to 3, wherein the first body portion is a tail portion and the second body portion is a head portion.

5. A method according to any one of claims 1 to 3, wherein the first body portion is a head portion and the second body portion is a tail portion.

6. A method according to any one of claims 1 to 3, wherein the first body portion is a head and tail portion and the second body portion is located around the head and tail portion intermediate the ends thereof.

7. A method according to claim 4 or 6, wherein the second maximum diameter portion is located behind the first maximum diameter portion.

8. A method according to claim 5 or 6, wherein the second maximum diameter portion is located in front of the first maximum diameter portion.

9. A method according to any one of claims 1 to 8, wherein the second maximum diameter portion is provided by the first body portion.

10. A method according to any one of claims 1 to 8, wherein the second maximum diameter portion is provided by a disc- or ringlike member located between the first and second body portions.

11. A method according to any one of claims 1 to 10, wherein the pellet further comprises a third maximum diameter portion 16 -

12. method according to claims 5, 9 and 11, wherein the third maximum diameter portion is provided by the head portion.

13. A method according to claims 5 and 11, wherein the third maximum diameter portion is provided by the tail portion.

14. A method according to claim 5 or any claim dependent thereon, wherein the head portion has a rearwardly extending member which is received in a hole in the tail portion.

15. A method according to claim 14, wherein the hole in the tail portion is a through hole.

16. A method according to any one of claims 1 to 15, wherein the second maximum diameter portion has an annular forwardlyfacing face which is substantially perpendicular to the central axis and an annular radially outwardly-facing face which is substantially cylindrical.

17. A method according to claim 16, wherein the second maximum diameter portion has an annular rearwardly-facing face which is substantially perpendicular to the central axis.

18. A method according to any on, of claims 1 to 17, wherein the first body portion is made of metal.

19. A method according to claim 18, wherein the first body portion is made of a lead, copper and tin, bismuth or zinc alloy.

20. A method according to any one of claims 1 to 19, wherein the first maximum diameter portion has a bigger diameter than the second maximum diameter portion.

17 -

21. A method according to claims 12 and 20, wherein the first maximum diameter portion has a bigger diameter than the third maximum diameter portion.

22. A method according to any one of claims 1 to 21, wherein the second body portion has, at least adjacent to the first maximum diameter portion, a part whose diameter is substantially the same as the inner bore diameter of the unchoked part of the bore.

23. A method according to claim 22, wherein said part of the second body portion comprises an intermediate diameter portion adjacent to the first maximum diameter portion.

24. A method according to claim 23, wherein the intermediate diameter portion is axially located between the first and second maximum diameter portions.

25. A method of preventing the buildup of deposits of plastics material in a barrel of an air, gas or spring gun having a choked and rifled bore, the method being substantially as herein described with reference to, or with reference to and as illustrated in,-the accompanying drawings.

26. A pellet for use in a method according to any one of claims 1 to 25.