Abstract:
A small caliber armor-piercing bullet is described in which a case hardened steel nosed lead projectile is utilized to help reduce projectile fragmentation at impact.

Description:
The present invention relates to ammunition projectiles and specifically to small caliber armor piercing projectiles. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     In recent years, there has been an increasing tendency toward use by the military services of armored personnel carriers to transport infantry and helicopter gun ships, which are also armored to shoot at infantry. With this increasing use of armor, the rifle bullets of the relatively recent past are, in many cases, rendered relatively ineffective due to their inability to effectively penetrate light armor. Two recent small caliber ammunition (.50 caliber and under) developments have changed the situation somewhat. The first is the reintroduction of the steel nosed lead bullet in such forms as the new NATO 5.56 mm round (called the &#34;M855 by the U.S. Army). The second is the development by Winchester (Olin Corporation) of the first truly effective 7.62 mm and .50 Caliber (12.7 mm) Saboted Light Armor Penetrating rounds. The new Olin SLAP rounds have proven extremely effective while the somewhat rounds have proven extremely effective while the somewhat more inexpensive NATO round has proven to be a significant improvement over the prior 5.56 mm ball round. It would seem that little further could be done to improve the  5.56 mm round, since 5.56 mm is too small to reduce its caliber further to give a saboted round, except perhaps to single flechette, and as yet flechette rifle rounds have all been abandoned as unseccessful. 
     However, when Winchester attempted to duplicate the M855 round, some unexpected results occured. The Winchester version consistently outperformed the NATO round. In view of this, further experimentation was done to determine the cause of these unexpected results so that the improvements could be introduced into the round. It will be understood that since the M855 round is designed to penetrate armor, the more armor the round can penetrate the better. Thus, surprisingly, a heretofor unrecognized problem was discovered in the existing round and the penetration ability of the round greatly improved. 
     The improved penetration ability is achieved by the present invention which provides for case hardened steel noses for the round, the hardness of the nose being Rockwell C50 minimum at a depth of 0.030 inches, with the interior of the nose being below Rockwell C50in hardness. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will be better understood by reference to the attached FIG. 1, which is an axial cross section of the nose portion of the projectile of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It is seen that the projectile 10 includes a lead body 12 having its forward portion in a secant ogive, although any other suitable ogive could be used. In front of body 12 is a frustoconical steel insert or nose 18 which has a secant ogival exterior surface and a flat front end 20. Body 12 and insert 18 are encased within a cupronickle 16 which has a pointed tip 17 defining a conical air pocket 22 immediately in front of insert 18 inside of jacket 16. The flat front end of steel insert 18 allows projectile 10 to penetrate armor at greater obliquity than would be the case if steel insert 18 had a pointed nose because the front corners of steel insert 18 can dig into the surface of a metallic target whereas a pointed nose would tend to be deflected. 
     Steel insert 18 is additionally surface or case hardened to a minimum of Rockwell C50 at a depth of 0.030 inches in order to give the insert increased hardness relative to the armor plates against which it would be expected to be used. For example, standard NATO armor plate has hardness of RB 55-70. Increasing the hardness of the nose portion of a projectile is not something that is lightly done. There is a strong belief, found throughout the prior art, that hardening the nose of a projectile is a bad thing to do because it increases the brittleness of the nose portion which portion sees the highest impact forces as the projectile strikes the target (see for example U.S. Pat. No. 1,398,229). In fact, seen in the test data below, simply hardening the entire nose portion results in projectile fracture on impact. Thus, the basic thrust of the prior art has been to soften the nose portion relative to the remainder of the projectile so that these initial impact forces are cushioned and can be received without breaking the nose of the projectile. However, this makes the projectile nose tend to deform (squash) on impact which reduces sharpness and hence the cutting action (sectional density) of the projectile on impact. Contrary to this belief, applicant has increased the hardness of the nose while leaving the interior of the nose somewhat softer with unexpectedly improved results. In comparative tests against the same armor plates, it has been found that the nose or tip of the relatively softer steel insert of the current M855 round breaks off in test plates and thus increases the frontal area of the projectile so much that penetration is often prevented. In contrast, the case-hardened steel insert of the invention penetrates the same plate without any evidence of deformation of the steel insert. In order to conform the unexpected results of the invention, the following example containing six (6) tests is provided. 
     EXAMPLE 
     Samples: 
     I--E.O. 4443-AISI 12L14 Rc50 min. @0.030&#34; depth, Steel Insert (the invention) 
     II--E.O. 4443-AISI 4140+Te Rc46-48, Steel Insert (Through Hardened) (conventional 5.56 mm NATO) 
     III--E.O. 4443-AISI 4140+Te Rc54-57, Steel Insert (Through Hardened) (hardened version II) 
     Bullet Weights: N=20 
     
         ______________________________________  Weight (grains)Sample   Avg.           Max.   Min.______________________________________I        62.0           62.3   61.6II       62.0           62.2   61.6III      62.0           62.3   61.6______________________________________ 
    
     Loading Data: All samples 
     Shellcase--5.56 mm Current Production 
     Primer--41-257W 
     Powder--WC844 SM547@26.7 grs. 
     Bullet--See above 
     Loaded Length--2.250±0.010 inches 
     Crimp--Collect four segment 
     Bullet Pull--140±20 lbs. 
     Bullet Pull: N=5 
     
         ______________________________________   Pull (lbs.)Sample    Avg.          Max.   Min.______________________________________I         143           151    121II        134           142    126III       143           156    125______________________________________ 
    
     Results: 
     Accuracy: Barrel No. Z-10, Range 200 yards, 10 shot groups. 
     
         ______________________________________             Accuracy (in.)Sample Group   Velocity @ 15&#39; (fps)                       MR    ES   EV   EH______________________________________I     1                 3077   .99  2.20 2.15 2.20 2                 3076  1.00  3.50 2.70 3.00 3                 3074  1.87+ 6.85 6.30 4.75 4                 3075   .84- 2.80 2.45 1.45 5                 3084  1.25  4.20 2.10 4.20         Average   3077  1.19  3.91 3.14 3.12II    1                 3075  2.99  8.60 6.35 8.60 2                 3061  2.90  8.80 7.70 7.30 3                 3071  2.82  7.25 7.10 6.70 4                 3069  2.49  7.40 3.35 7.30 5                 3062  2.92  9.50 8.55 5.45         Average   3068  2.82  8.31 6.61 7.07III   1                 3077  2.52  8.15 7.15 6.25 2                 3065  3.14  8.40 8.10 6.05 3                 3074  2.09  6.70 6.60 3.85 4                 3072  2.63  8.40 6.15 7.70 5                 3065  2.49  7.50 4.45 7.40         Average   3071  2.57  7.83 6.49 6.25______________________________________ 
    
     Penetration Tests: 
     Test No. 1 
     Plate--0.415&#34; SAE 1020 Hot Roll 
     Velocity--Muzzle Velocity approximately 3085 fps 
     Range--100 meters 
     Gun--Accuracy Barrel Z-10 
     Results (Continued): 
     Penetration Tests (Continued): 
     
         ______________________________________Sample No. of Rds.            Penetration    Comment______________________________________I     10         10 - CompleteII    10          0 - Complete  Recovered Insert             3 - Broke back of                           showed front 1/2              plate.       broken away.III   10          3 - Complete  Recovered Insert             5 - Broke through                           showed front 1/3              back of plate.                           broken away.             1 - Broke back of              plate.             1 - Incomplete______________________________________ 
    
     Test No. 2--Same as 1 but fired in M16A2. 
     
         ______________________________________Sample No. of Rds.            Penetration    Comment______________________________________I     10         10 - CompleteII    10          0 - Complete  Recovered Insert             1 - Broke back of                           showed front 1/2              plate.       broken away.             9 - IncompleteIII   10          1 - Complete  Recovered Insert             3 - Broke through                           showed front 1/3              back of plate.                           broken away.             3 - Broke back of              plate.             3 - Incomplete______________________________________ 
    
     Test No. 3 
     Plate--Nato Plate Configuration, 10 Ga. (0.138&#34;) SAE 1010, 1020, R B  55-70 and 0.020&#34; Aluminum Witness Plate 6 inches behind. 
     Velocity--1500 fps 
     Range--644 meters (simulation) 
     Gun--Accuracy Barrel No. Z-10 
     Results (Continued): 
     Test No. 3 (Continued): 
     
         ______________________________________ Number   15&#39;Sample of Rds.  Velocity Penetration                              Comment______________________________________I     10       1498 fps 8/8 - Complete*                              2 shots not                              counted. Not 1                              caliber apart.Complete*      1496 fps  5/8 2 shots notIncomplete               3/8 counted. Not 1                              caliber apart.                              Recovered                              Inserts show                              deformation of                              front 1/3.III   10       1512 fps  10 - Complete*______________________________________ *Complete Penetration  Both Plates Perforated. 
    
     Test No. 4 
     Plate--Nato Plate configuration (see above) 
     Velocity--1300 fps 
     Range--744 meters (simulation) 
     Gun--Accuracy Barrel No. Z-10 
     
         ______________________________________Sam- Number   15&#39;ple  of Rds.  Velocity Penetration                            Comment______________________________________I    10       1325 fps 10 - Incomplete                            Recovered Insert                            shows no defor-                            mation.II   10       1337 fps 10 - Incomplete                            Recovered Insert                            shows deformation                            of front portion.III  10       1306 fps 10 - Incomplete                            Recovered Insert                            shows no defor-                            mation.______________________________________ 
    
     Results (Continued): 
     Test No. 5--Same as 4 but Range 709 meters (simulation). 
     
         ______________________________________Sam- Number   15&#39;ple- of Rds.  Velocity Penetration                            Comment______________________________________I    5        1325 fps 5 - Complete*II   5        1294 fps 5 - Incomplete                            Recovered Insert                            shows deformation                            of front portion.III  5        1327 fps 4 - Complete*                            No deformation of                  1 - Incomplete                            Insert.______________________________________ *Complete Penetration  Both Plates Perforated. 
    
     Test No. 6--Same as 4 but Range 714 meters (simulated). 
     
         ______________________________________Sam- Number   15&#39;ple  of Rds.  Velocity Penetration                            Comment______________________________________I    4        1323 fps 3 - Complete*                            No deformation of                  1 - Incomplete                            Insert.II   5        1329 fps 5 - Incomplete                            Recovered Insert                            shows deformation                            of front portion.III  5        1315 fps 5 - Incomplete                            No deformation of                            Insert.______________________________________ *Complete Penetration  Both Plates Perforated.