Lack of Marks #2

[yamoon]

I posted 12-26-2019 a post with several photos of a Mauser sporter, the post is titled “Lack of Marks”. I have been trying off and on for over 2 years to work up a hand load using Hornady .321 165gr spire point, most of the groups are 4” and larger. I came across a post on the Nitro Express forum yesterday about an 8x60 marked 815 indicating a .321 bore. My rifle has only 7.7mm marking but a .321 bore, I checked some fired brass from this rifle and a .323 bullet slips in easily, Axel indicated .323 bullets should not be a problem. The bolt from this rifle has a small s on the bottom, does this signify an s chamber? I checked another Mauser sporter that is a .318 bore and it does not have the s. I have 140 rounds of Priv Partizan 196 gr factory ammo I am going to try. This rifle has a 20 1/4 inch barrel to the bolt face and weighs 6 1/2 pounds empty without the scope and 7lbs 2oz with the scope. I want to hunt with it so I am hoping the switch to .323 will work out.
Mike

[mike ford]

Mike,
I went back to your old post an noted a couple things. The barrel is marked M88. 8. Original M88 rifles often had barrels with .321" groove diameter (I'm guessing when you say bore diameter you mean groove diameter). Also, in that post you reported the fired cases would accept .321" bullets but not .323". Now you say .323" bullets will slip in. I often use this test myself and know from experience that you must check this again whenever you change cases. One manufacturer's case may clear the larger case and another's not. I find this more often with cases formed from a different donor case. The original M88 bullet weighed around 227gr. and your rifle may be throated for a bullet much longer than the 165gr. one you have been using. If the throat is longer than the bullet, you might have accuracy problems from the bullet being unsupported before it engages the rifling. As a general rule, 196gr and 198gr bullets don't have this problem. Other 8mm I diameter barrels often give satisfactory service with .321" commercial bullets if the throat is not too long for the particular bullet. The to find out is just what you are doing- try.
Mike

[yamoon]

Mike
I originally fired a hand loaded .318 and checked the case, I checked several cases that I fired .321 hand loads and the 323 bullet slips in easily.

[Axel E]

Mike, which Prvi Partizan loads do you have on hand. PPU catalogs two different loads, both loaded with the same .323” 196 soft point bullet. In the cartridges labeled 8x57 IS they are loaded to European CIP standards, mv 2460 fps. Their 8mm Mauser labeled cartridges are loaded to emasculated American SAAMI standards, mv 2182 fps. The latter may be used in any 8x57, I or S bore rifle, but the full power CIP loads may be used in your rifle too.
Your rifle was built on a 1912 action by the Mauser, Oberndorf, factory that was sold as “action only” to an unidentified Suhl gunmaker. As the rifle was barreled, stocked and proofed in Suhl for retail by Schikora, you cannot expect Mauser factory markings on the barrel. An interwar years owner apparently followed the 1934 RWS advice and had chamber and throat altered to take S loads. The small s on the bolt is certainly not related to this alteration.
In the interest of other readers, here is what I posted on the topic years ago on nitroexpress forum:
The differences between 8mm I (.318") and 8mm S (.323") cartridges as well as minimum bore dimensions were only fixed by the 1939 proof law. As both the Austro-Hungarian army in WW1 and P.O.Ackley in the 1950s found out, it is not the too tight bore that causes excessive pressure, but the chamber and throat dimensions. A max S cartidge in a minimum I chamber has neck and bullet wedged into the neck and throat area of the barrel. On firing the case neck cannot expand and release the bullet and the bullet, wedged into the barrel throat, cannot move until pressure has risen to danger levels. Mauser was well aware of this fact. In Jon Speed's first book, "Mauser OOSR" on page 275 a hand written table from the factory about sporting rifles bore dimensions is shown, dated December 9, 1926. 8mm bore dimensions given here are clearly I, .318" ones. But on the bottom of this table there is a footnote. Translated into modern English parlance it reads:
"The sporting rifles for the 8x57 and 8x60 cartridges get the throat for the S bullets, so that the S-type (.323") cartridges may also be used."
IIRC Finn Agaard for many years used an 8x60 normal (I bore, .318") B Mauser in his early Kenya years until the barrel was shot out. The only ammo he got was 8x60S H-jacketed loads, the highest pressure RWS loads that in 1940 set the maximum allowable pressure for 8x60S loads. He never noticed indications of excessive pressure. Nor do I when using 8x60S factory loads in my own 8x60 NORMAL marked B Mauser of 1934 vintage.
The legal difference between I and S bores was only fixed with the 1939 proof law. Before, different solutions were offered, even by the ammunition factories. Two lengthy quotes, sort of translated by myself:
1934 RWS handbook, page 38:
" If you want to shoot the thicker S loads from a rifle that was originally intended for the 8x57I or 8x57IR with long round nose bullets, don't fail to have your chamber and throat reworked by a gunsmith. Failing to do so may result in excessive pressure."
The Suhl and Zella-Mehlis gunmakers used their chambering reamers as long as possible, resharpening them several times. Without set minimum chamber dimensions this practice sometimes resulted in rather small chambers and throats. As long as a 8mm I cartridge slipped into the chamber and the thing stood proof, it was deemed ok.
The 1940 RWS handbook contains these suggestions:
"As in modern bolt action rifles rarely any accident is known, the rimless 8x57 and 8x60 cartridges will be loaded with S bullets (.323") only. Modern powders allow us to keep the pressure below dangerous levels without changing the ballistics. Other with the rimmed versions: As the rifle barrels of older drillings and combination guns are much thinner, there may be a danger here. So the old 8x57IR should be loaded only with I (.318") bullets in the future. The (then) rare S barrel guns may live with slightly diminished accuracy. The 8x60R should be loaded with S bullets only. This leaves just one problem, the 8x60RS MAGNUM loads. These loads should be sold only with prominent warnings on the package: "for S diameter , 7.89 / 8.20 mm barrels only!" The individual cartridges will be marked by a black primer and knurling of the rim."
So, if you want to use S, .323" bullets in your I bore M98 rifle, do these two checks:
take a case fired from your rifle, unresized of course. If a .323" S bullet easily slips in and out the neck, the neck area of your chamber is sufficiently wide. Next, check the bullet seating depth. The bullet should be able to move at least 5mm / .2" before it engages the rifling.

[yamoon]

Axel
thank you for the information, I read both of your posts on the Nitro Express forum, the recent one and the 2013 forum. I now believe the reason the .323 would not enter the neck was because I used a moderate .318 hand load and do to gas leakage with a .318 bullet the pressure dropped as the projectile exited the case and the case neck did not expand fully. I am going to do a chamber cast before firing the Parvi Partizan rounds, they are the 8mm marked box. I hope to find a load this rifle likes as it should be a joy to carry in the field.
Mike
did a chamber cast, everything looks fine to shoot the PPU ammunition.

[yamoon]

Tried the rifle with Parvi Partizan .323 196gr ammunition. Shot with no pressure signs 1st three rounds grouped under 2 inches next 2 were 4 inches high, it dawned on me that this rifle has a very light weight barrel, after it cooled down it was back on target. I doubt I will fire enough in a hunting situation to heat the barrel..
Mike

[mike ford]

Mike,
I agree with you about not overheating the barrel in a hunting situation, infact I now have a habit of only loading two cartridges when hunting with a bolt action rifle. It is just easer and I learned that you either don't have enough time for a third shot or you have enough time to load the third one from the reserves. Everyone cultivates his own habits.
Mike