The World of Computer Software/World_Of_Computer_Software-02-387-Vol-3of3.iso/7/76239lod.doc

Text File | 1993-03-02 | 18KB | 371 lines

                     SUMMARY DATA ON 7.62x39
                     - Revised CEH 4-23-90 -

This is additional data which was not included in the recent
American Rifleman article.

     I have reloaded thousands of rounds of this 7.62X39
ammunition with both cast bullets and jacketed, and have fired
them in the AK and the SKS. I got frustrated with the AK as
accuracy of these seems to be generally poor, but the SKS is more
reasonable, and is a real bargain these days. It seems the best
an AK will do is about 5-6 moa, and the SKS with good ammo will
do 3-4, sometimes better. The gas ports on these guns are larger
than they need to be for reliable functioning, so light cast
bullet loads down to about 1400 f.p.s. work fine. None of the
common cast bullet designs are quite right for this caliber,
because the necks are so short, and the groove diameters run
large.

     I designed a bullet and had a custom mould made by NEI of
Canyon City, OR, which they identify by the number 155.311GC.
This bullet is .92" long and weighs 155 grs. in linotype or about
160-grs. in wheelweight alloy. I designed it with the idea to
produce the heaviest bullet which could be loaded effectively
without the GC poking into the powder space, and which would be
big enough on the forepart to fill the large throats on the AK
and SKS, as well as in the 7.62x54R Russian, .303 British, 7.65
Argentine, 7.7 Jap, etc. It has only one grease groove, and a
crimp groove .26" from the base. The rear driving band casts
.313", the front band .311" and the forepart ahead of the crimp
groove is .310", and the ogival radius starts from this large
diameter in order to maximize bearing length. The bullet has
proven very accurate, and outshoots ball ammo in the SKS or AK
with any reasonable load, and in a bolt action rifle will stay
under 1-1/4" 10-shot groups at 100 yards taking bullets out of a
5-cavity gang mould.

     The Sierra 125-grain .308" spitzer seems to be the most
accurate of this weight, and shot better than the Hornady 123-
grain .310" and the 150-grain Spire Points in either .308" or
.312", which they make for the .303 British. The popular 150-
grain spitzers intended for the .30-'06 or .308 do not expand at
7.62x39 velocities, but bullets intended for the .30-30 work
well. Of these the 125-grain Sierra JHP flatnose and the 130-
grain Speer FN seem to work the best. I have gotten good accuracy
with the 150-grain Sierra MatchKing bullets in by boltgun of this
caliber which I built on a Sako action, but you might consider
using match bullets a costly absurdity in an AK or SKS.

     I also tried some of the cheap surplus 7.62 NATO M80-type
bullets, but these shot very poorly, about 4-5" in the boltgun at
100 yds., and almost twice that in the AK, and about 6" in the
SKS. I prefer cast bullets for most of my shooting in this
caliber, but if I were to buy jacketed bullets the 125-grain
Sierras in either FN or spitzer style would be my choices, with
the 130-grain Speer flatnose .30-30 bullet also strongly in the
running, and the 123-grain Hornady spire point for the 7.62x39 is
also OK, as are 150-gr/ .30-30 bullets.

     I don't have the pressure gun to work with which I did when
at Ruger, but in my experience with several rifles, these loads
should be OK. When I did pressure tests with H322 and Accurate
Arms 2230 and Hodgdon H335 it appeared you couldn't get enough
into the case with a 125-grain bullet to get into any trouble,
and a caseful made a highly satisfactory load. H322 used to be
about the cheapest powder around, and works very well in this
caliber. I use 28 grs. with a 125-grain bullet for about 2200,
and 25 grs. with a 150-grain bullet for about 1900. With my cast
bullet I use 24 grs. for about 1850, which works very well.

     Accurate Arms now has their powder AAC1680 which is very
similar to the Olin 680 Ball powder, though slightly slower. The
best load with 1680 and the 155 grain NEI cast bullet seems to be
around 16 grs. in the SKS, which gave me about 1400 f.p.s., and
3" groups at 100 yds. 18 grs. gives 1630 f.p.s. and about 4"
groups in the SKS, with 19 grs. velocity is about 1700 and groups
opened up to over 5", which I consider unsatisfactory. I did just
two strings with the Olin 680 for comparison with the NEI bullet
at 18 and 19 grs., respectively, which gave 1810 and 1930 f.p.s.
I would not exceed 19 grs. of Olin 680 with the 155-grain cast
bullet, or 23 grs. with a 125-grain jacketed one, as these are
both full loads. With ACC2230 you can use all the powder the case
will hold with a 125-grain jacketed bullet, about 30 grs., and no
problem. With a 155-grain cast bullet start around 26 grs., up to
28 grs. maximum, for 2050 f.p.s.

     I have also used IMR-4895 with good results. About 17 grs.
is the minimum charge which will function the SKS with a 160-
grain cast bullet, but you can stuff the case with all the powder
it will hold and you can't get in any trouble. It works well with
cast bullets from 150 grs. up.

     As for reloading the Berdan primed cases, it isn't worth the
trouble.

     Charge Establishment for NEI 155.311GC cast CEH design
bullet, WW alloy quench-cast from mould, as-cast dia. .313",
tumble lubed in Lee Liquid Alox. No GC used except where noted.
Midway cases, Remington 9-1/2 primers, Ctg. OAL 2.20" taper
crimped in C-H die from Midway Arms. Test firings in Norinco AKS
with 16.4" barrel.

 H4198    Velocity     Remarks
 (Grains)  @ 15 ft.
  14.8     1252, 39Sd  feeds, ejects OK, but unburned powder
                       granules cause occasional failures
                       of breech to close fully.
  17.4     1490, 47Sd  functions OK
  18.5     1578, 31Sd  functions OK
  20.4     1715, 47Sd  function OK, slight leading w/o GC
  22.0     1880, 30Sd  GC bullet, function OK, no leading
  22.6     1909, 27Sd  GC bullet, function OK, no leading
                       accuracy decays above this charge.


Charge Establishment for Accurate Arms 1680 propellant in SKS
with NEI 155.311GC bullet, as above.

Grains     Vel. @ 15'   ES for 5-shot group @ 100 yds., (cm)
16.0      1422, 21 Sd                               4.5 cm
17.0      1629, 25 Sd                               7.7 cm
19.0      1710, 7 Sd                                11.7 cm

Olin W680 for comparison
18.0       1810, 15 Sd                    no group recorded
19.0       1932, 18 Sd                    "   "    "

Olin 680 with 122-gr. PS Ball bullet pulled from 101-71 Chicom
ammo.
23.0       2381, 11 Sd    Midway case with large primer F210
23.0       2332, 14 Sd    BELL case with small primer F205

PS Ball for comparison, velocities from SKS with 20.5" barrel
Chicom 101-71                             2415, 11 Sd
East German 04-77                         2448, 11 Sd


            MANUFACTURER'S CODES FOR 7.62X39 MM AMMUNITION
             CODE COUNTRY            CODE    COUNTRY
             01   WEST GERMANY       A79  SOUTH AFRICA
             3   USSR                AD   INDONESIA
              04   EAST GERMANY      aym  CZECHLOSLOVAKIA
              05   EAST GERMANY      bxn  CZECHLOSLOVAKIA
              10   BULGARIA          CAVIM  VENEZUELA
              11  (PRC no serifs)
                  Yugo has serifs
             13   CUBA               CBC    BRAZIL
             17   USSR               FN     BELGIUM
             21   POLAND             HP     AUSTRIA
             22   ROMANIA            IK   YUGOSLAVIA
             23   HUNGARY            IZ   CZECHLOSLOVAKIA
             31   PRC                Lapua  FINLAND
             031  PRC                NK   YUGOSLAVIA
             51   PRC                (letter N backwards)
             60   USSR               nny  YUGOSLAVIA
             61   PRC                PMC  SOUTH KOREA
             71   PRC                PMV  CUBA
             81   PRC                PP   YUGOSLAVIA
             93   NORTH KORE
             101  PRC
             141  PRC                PPU  YUGOSLAVIA
             270  USSR               PT   FINLAND
             343  POLAND             VPT  FINLAND
             351  unk.  (PRC?)       RPR  ROMANIA
             501  PRC                SO   FINLAND
             539  USSR               ZV   CZECHLOSLOVAKIA
             711  USSR
Numeral headstamps containing the number 1 (one) WITHOUT SERIFS
are usually PRC.

                EAST-BLOC BULLET TIP COLOR CODES:
           Tracer - Green  API - Black tip/red ring
                           API - Black tip/black annulus (PRC)
       PRC API will have lacquered or copper washed steel case.

      BRASS CASE WITH THIS CODE and nny headstamp is Yugo proof

     Analysis of 7.62x39 mm powder from Chinese PS Ball Factory
71, 1983: Is single-base, containing 0.4% K2NO3 flash retardant
bulk density .90 grams/cc, cylindrical grains .041 long, .0205"
diameter, NOT perforated, diphenylamine stabilizer, compares most
closely to IMR4475 in granulation and burning rate.


ACCURACY TEST OF 7.62x39 mm SKS RIFLES BY CEH 1/30/88

     Average of four consecutive 10-shot groups at 200 yards,
iron sights. Two targets each rifle shot with Yugo M67 123-grain
lead core ball Two targets each rifle shot with PRC 101-71 Type
PS steel core

Rifle No.    Origin     Avg. ES     No. of Hits on "E" Silhouette
641991      USSR pickup   11.75 33x40  (rifle condition
worn/good)

Note:     If zero had been 1/2 mil left this rifle would have
          scored 40x40 hits.

J8138     USSR pickup   11.38       38x40  (rifle condition
                                             worn/good)
M3976     USSR pickup   13.77       35x40  (rifle condition
                                             worn/good)
15082     PRC           15.16       37x40  (rifle condition
                                             excellent)
25636     PRC           12.17       35x40  (rifle in new
condition)

01724     PRC           12.72       39x40  (used, VG condition)
Avg. six  SKS rifles    12.82       36x40  90% hits

RESULTS BY AMMO TYPE: SIX RIFLES POOLED, 12 TEN-SHOT TGTS. @ 200

Chinese PS Ball         12.70       108x120 = 90%
Yugo M67 Ball           12.89       109x120 = 90%
25636  RESHOOT 300 YDS. 17.28       29x40  40 rds. PS ball 101-71
     This is typical 300 yd. performance for SKS
Previous Test of USSR SKS carbine serial no. 641991 by CEH and
JBR, March, 1983, average of five consecutive 5-shot groups at
200 yds.

               Vel.@15'   Smallest    Largest    Average
USSR PS        2297       7.50        12.87      10.59
60-K (1950)      31 Sd                         10-shot tgts.

This USSR PS test shows good agreement with other firings of SKS
rifles of 1/30/88, which included this one. Note influence of
ammunition quality below:

Lapua Ball     2370       3.31        7.50        5.94
(Berdan)       Better than typical
               SKS with PS Ball.


CEH FIRINGS OF AKM FOR COMPARISON WITH SKS

AKM Factory 66 #305163    17.25       32x40  (rifle condit.
                                             excellent)
PRC 101-71 PS Ball shot at 200 yds., typical for AKM and AK47.

Previous CEH test of Maadi AKM imported by Steyr for NRA, March,
1983.

Average of Five consecutive 5-shot groups at 200 yards.
               Vel.@15'  Smallest    Largest     Average
Lapua Ball     2379       7.20       9.60        8.66
(Berdan)         12 Sd

     This performance is better than expected of PS Ball in
average AKM and AK47, attributable to better quality of Lapua
ammunition. Note ammunition comparison  with SKS above, refiring
the same rifle in Jan., 1988, compared to 1983 results.


          U.S. Military Specification Mil-C-70760
          Ctg. 7.62x39 mm, Commercial
          Dwg. #12598661

Bullet extraction force:  60 lbs. min.
Accuracy:                 5.0" max. MR @ 200 yds.
Velocity:                 2275 +/- 30 f.p.s. @ 78', Sd 30 max.
                         (eq. to MV = 2350 f.p.s.)
Chamber pressure:         45,000 psi (Cu) max. avg.
Cyclic Rate:              550-750 r.p.m. in AK-47/AKM rifles.
Bullet Wt.                124 grs., lead core with copper alloy
                          or gilding metal-clad steel jacket.
Primer:                   non-corrosive

Penetration Tests of 7.62x39 mm Ammunition by CEH Oct., 1986. All
firings at 50 yds. range against standard CMU ("cinder block")

WEAPON  CAL.   AMMUNITION               TEST RESULTS
AKM  7.62x39mm  Yugo M67      Block hit end-on, perforated web,
bullet
                lead core     broke up and only marked next
layer.
                Chinese PS    Block hit end-on, perf. first and
                steel core    second webs, cratered third
                              web, without cracking it.

AR-15  5.56     M193          Block hit end-on, perf, first web
             lead core       and broke up, marked 2nd next web

                M855          Block hit end-on, perf. first and
                steel core    second webs leaving no damage to3rd
                              web other than deposit of debris.
                              Repeat test of M855 broadside hit
                              gave complete perforation both
                              sides of CMU, spraying witness tgt.
                              3 ft. behind with fragments, steel
                              core penetrated 3/8" into 1x2 SYP
                              tgt. frame.

Garand .30-'06  Ball M2       hit end-on perforated first and 2nd
                lead core     second webs of CMU, heavily
cratering
                              third web, and cracking lengthwise.

      TYPICAL DISPERSION OF SELECTED SOVIET AND U.S. RIFLES

     Approximate Extreme Spread for 10-Shot Groups, Estimated
from Measured  Radial Standard Deviations, (assuming MR as .9xRSd
and ES as 3xMR) NRA Master gunners in favorable conditions
adapted from U.S. Army APG data, AMSAA Technical Report No. 440 ,
May 1987.

          7.62x39   5.45x39   5.56x45   5.56x45
          USSR PS   USSR PS   US M193   US M855
RANGE:    AK-47     AK-74     M16A1     M16A2
(metres)
100       4.8       3.5        2.7       2.7
200       9.6       7.0        5.5       5.5
300       14.4      10.5       8.9       8.6
400       19.6      14.9       12.8      11.9
500       25.0      19.6       17.6      16.0
600       30.6      25.5       23.0      20.4

DOCTRINAL
BATTLE-SIGHT
RANGE     300       450        250       300(metres)

Firing table for 122-grain Type PS Ball, GMCS mild steel core BT
C7 :.156, Standard Metro, adapted from Soviet and U.S. Army Data

Range    Velocity   Energy     Drop     Elev.    Max. Hgt.
(yds.)   (fps)      (ft.-lbs)  (ins.)   (moa)     (ins.)

0         2340      1483       0         0-          1.5
100       2080      1172       3.5       5           0.3
200       1836      913        14.9      8.2         3.5
300       1606      699        37       12.8         9.9
400       1388      522        72.4     18.5         20.9
500       1190      384       126.5     25.6         38.7
600       1051      299       206.9     34.7         65.9

EFFECTS OF TRAINING AND DOCTRINE ON INFANTRY RIFLE EFFECTIVENESS

     U.S. doctrine is that the M16 rifle be carried habitually
with the sights set to the BSR unless there is a need to set the
sights for some other range and there is time to do so. American
GI's are taught to aim at the center of mass of the visible
target at all times, which centers the densest portion of the
round to round shot dispersion in the center of the target, to
maximize hit probability. Soviet doctrine is to use a bottom of
target point of aim with the sights set at the BSR at ranges up
to 300 metres, and to set the sights for the estimated range at
longer distances. In operational situations the type and
magnitude of other system errors cancel any effect of wind
deflection upon hit probability for the average soldier. The
intrinsic single-shot round-to-round dispersion of the AK47 is
larger than the newer AK74, but both Soviet rifles have a larger
intrinsic RRD than either the M16A1 or M16A2. These differences
are not meaningful in most operational combat situations because
stress is the great equalizer. If the shooter's error approaches
the worst hitting performance seen in peacetime field experiments
the differences in being able to hit an "E" silhouette target
caused by differences in inherent weapon accuracy are wiped out.
If effective range is gaged by single-shot hitting performance of
average soldiers in combat situations, the AK47, AK74, M16A1 and
M16A2 have almost no difference in performance. In US Army
testing of the AK-74 rifle it was found that the time to hit was
the same for the AK-74 and M16A1 for target exposure times of 2-
3.5 seconds, but that the muzzle-break-compensator of the AK-74
was an aid to improving hit probability at close-range targets
with burst fire. The third round in a burst from the M16 seldom
if ever hits anything and is nothing more than a waste of
ammunition. Personnel should be taught to use two-round "double-
taps" for close range engagements within 50 yds. Beyond 50 yards
rapid semiautomatic fire is far more effective than any type of
automatic fire, in being able to obtain hits, as well as in
conserving ammunition.