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All 7.9 X 57 (8 X 57) Are Not Created Equal

Dave Emary

 

There are a number of 8mm surplus military rifles on the market at present. Including those that have been offered in the past there are a tremendous number of different types and manufacturers of rifles that are all lumped into the designation 8 X 57. Although it is true that the vast majority of these rifles were intended for the same .323 diameter bullet, these guns are not all the same when it comes to the bore/groove and throat dimensions. These differences can cause significant differences in operating pressure of ammunition from what the hand loader or manufacturer intended. The following information applies to rifles manufactured in the WWII time frame for the 7.9 X 57 JS, .323 diameter projectile ammunition.

            I began this work after developing loads that were fired and pressure tested in a German made K98 rifle. These same loads were then fired in a G 33/40 and a VZ 24 and showed all the signs of excessive pressure. After looking carefully in the barrel of these rifles it was obvious their rifling form was substantially different than that encountered in the German made rifles. The SAAMI and CIP minimum specifications for bore, groove and land dimensions call for a bore of .311, grooves of .323 and a land width of .078. A large number of rifles, representing a good cross-section of manufacturers, were slugged to see what actual dimensions were used

Five German made rifles, four of which were standard K98s, one having a Czech manufactured DOT barrel,  and the fifth rifle, a late war HK converted Carcano in 7.9 X 57, were slugged.  The barrels ranged from Good + condition to the HK Carcano with a virtually new bore. All guns had bores in the range of .3115 - .3125, grooves from .3233 - .3243 and land widths from .063 - .065. The length of cartridge at which a Hornady 195 gr SP hit the lands varied from 3.180 to 3.260 mainly a function of barrel condition. The data generated for the Hornady 195 gr SP was generated in one of German  K98 rifles

Three Yugo K98 rebuilds were slugged and their bores measured .3109 - .3113, groove diameters were .3231 - .3233, and land width ran from .063 - .065. There was a tremendous variation in throat length at which the Hornady 195 bullet hit the lands. Two rifles were in the 3.230 3.250 range. However, one rifle had the bullet hit the lands at 2.975. This rifle also lacked one thread on the shank. The barrel had obviously been set back and the shoulder moved back out without throating the gun. All three barrels appeared to be in very good to nearly new condition.

Four Turkish M38 barrels were slugged. All barrels appeared in good to very good condition. There was a tremendous variation in bore dimensions. Bore dimensions varied from .3108 - .312, groove dimension varied from .3231   .3258, land width varied from .083 - .085. Throat depth was not checked on these rifles.

Two Italian manufactured M38 type Carcano rifles, originally made in 7.9 X 57 were slugged. Bore dimensions measure .3111 and .3112, groove dimensions were .3231 and .3232, land width was .078. The Hornady 195 SP hit the lands in these rifle at 3.135 and 3.180. It is interesting to note the bore dimensions in these rifles were nearly identical to the current CIP specifications. Both of these rifles were in virtually unfired condition.

Two Czech manufactured G24(t) rifles, a G 33/40 and a VZ 24 were slugged. The Czechs used a different rifling specification as these rifles had tremendously different bore dimensions. The bore dimensions ranged from .3090 - .3095, Groove dimensions varied from .3263 - .3270, land width was .145. Only the G 33/40 was checked for throat depth and the Hornady 195 SP hit the lands at a C.O.L. of 3.120. 

I am relating all of this information as  a caution to those of you shooting these rifles. Because of the differences noted in these rifles there could be a significant variation in chamber pressure that a given round of ammunition will produce in different guns. In particular if you have a rifle that is Czech manufactured, BE CAREFUL. You can easily wind up in a situation with some ammunition or reloading data that could lead to things such as pierced primers or leaking primers and ruined primer pockets. My advise to you with a Czech manufactured rifle would be to drop maximum loads that are listed in a K98 type rifle 3.5 4.0 grains for a maximum charge. The data in the Hornady reloading guide was developed in a German made K98 with a very good bore. The pressures were kept somewhat conservative though by no means low, 50-52,000psi. Pressures for European manufactured ammunition in this rifle shoots about 55,000 psi for current commercial and upwards of 57,000 for milsurp. These higher pressure loads and some published reloading data could lead to excessive pressure in these Czech rifles. 

For other rifles, Yugo, Turk and German K98s I recommend several quick checks prior to firing ammunition or setting up reloads. If you have calipers measure the C.O.L. of the cartridge before chambering a round or use a ruler and get the most accurate estimate you can.. With the safety on chamber the round.  Open the bolt and extract the round  and measure it again. If the round has been shortened or there are shiny marks on the ogive of the bullets, the bullets are touching the rifling lands or the lands have pushed the bullet into the case. I would recommend caution when firing ammunition that does this and if there are any signs of excessive pressure drop your charge weight or try another type of ammunition.

There is probably very little risk of anything catastrophic happening with any of the above situations in a rifle in good condition. It is the rifle with excessive headspace and dubious maintenance or condition that could cause something unpleasant.

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M.O.A

This information will serve as a guide to determine what level of precision you can expect from a K98, M48/A, or VZ 24 in reasonably good condition, with a variety of ammo types.  The MSA shooters who provided the target information range in experience from three years or less to several years and shooting at expert level.

If your recently purchased K98 has a good bore, the action is in safe and good plus condition, and fits well into the stock, you should expect to be able to shoot five-round groups of 1.6" to 5.4" at 100 yards depending on which type of ammo you choose to fire.

The first table below illustrates the aggregate results from several shooters. Below the table report is a general report by shooter/rifle to demonstrate how the tables were derived.

K98 8mm 100 yds 8 inch target-5 rd groups

                                                                                High                            Low                            Avg

                                    S&B                                    3.5"                            1.6"                            2.55"

                                    Turk                                    5.4"                            3.25"                          4.325"

                                    Yugo                                    5.3"                            4.5"                            4.9"

                                    Handloads                          -                                    -                                2.375"

 

M48/A

                                    S&B                                                                2.88"

                                    Turk                                                                7.719"

                                    Yugo                                                                4.5"           

                                    German                                                            3.625"

                                    Handloads                                                        2.875"

 

   VZ24  

                                     S&B                                                                4.25"

                                    General information

K98 1

                                                    S&B 196 gr

                                                    Tgt 1                       2.079

                                                    Tgt 2                       1.600

                                                    Avg                          1.839

 

                                                    K98 2

                                                    S&B 196 gr

                                                    Tgt 1                       2.077

                                                    Tgt 2                       1.759

                                                    Avg                          1.918

 

                                                    K98 3

                                                     S&B 196 gr

                                                    2 tgt avg                 3.25

 

                                                     Turk

                                                     2 tgt avg                 4.328

 

                                                    Yugo

                                                    2 tgt avg                 5.107

 

                                                    M48

                                                 S&B 196 gr

                                                2 tgt avg                 5.469

    

                                                Turk ammo

                                                2 tgt avg                 7.719

 

                                                VZ24 w/pistol scope

S&B

                                                2 tgt avg                 4.25

 

                                                Turk ammo

                                                2 tgt avg                 7.812

 

                                                K98

                                              Turk                        4.5

                                                Yugo                       5.3

                                                Handloads                2.375

 

                                                M48A

                                                Hornady 170 Rem case Varget 48 gr                       2.875

                                                S&B sp                                                                                  3.187

                                                German Milsurp 1935                                                       3.625

                                                Yugo milsurp                                                                        4.5

 

                                                BRNO K98 (new)

 

                                                Turk issue

                                                4 tgt avg                                                                                 4.06

 

                                                Sunny-snow cover/22F/wind ene 5kts/altitude 430 ft/baro 30.24 corrected for elev.

                                                T1=3.41/t2=3.79/t3=3.64/t4=5.4

 

           

 


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