What is the difference...


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P5 Guy
January 5, 2006, 12:07 AM
... and how can you tell which 8mm Mauser round is for which Mauser rifle?
I've read something about two different size bullets and do not remember what a JS (?) round is and what rifle it takes to shoot it?
Would a 1904 Portuguese need special round?

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Sunray
January 5, 2006, 05:12 AM
The Germans changed from a .318" bullet to a .323" bullet in 1905. The 'JS' is the .323" bullet. The 'J' uses the .318" bullet. They are not interchangeable. This is a pretty good explanation of the differences. Note the velocity difference.
http://en.wikipedia.org/wiki/8mm_Mauser
Your 1904 may or may not use the smaller bullet. Lots of Mauser using countries changed the barrels to use the bigger bullet and lots didn't bother. Slugging the bore will tell you which bullet to use. Hammer a .30 calibre cast bullet(a suitably sized lead fishing sinker will do) through the barrel with a brass rod and a plastic mallet, from the chamber end and measure it with a micrometer. You may have some difficulty finding 8 x 57J(aka 8x 57I) loaded ammo though.

P5 Guy
January 5, 2006, 09:25 PM
Thanks Sunray, I'll get the measuring done soon as I can.
I hope that this rifle isn't going to be hard to feed. It looks like it's brand new.

MNgoldenbear
January 7, 2006, 06:03 PM
If all else fails, you could always rebarrel for whatever you want to use out of it that's compatible with the magazine, bolt, etc. Good luck though. Hope it's the easier size to find bullets/ammo for. Much less hassle.

Vern Humphrey
January 7, 2006, 06:27 PM
Bore size should be the same, J or JS. What changed was bullet diameter and lede. The original idea was to shoot a bullet smaller than groove diameter, and the change to allow a groove-diameter bullet was made in the lede -- a barrel made for the J bullet will have higher pressure when shot with the JS bullet, because it is basically jammed into the lede when loaded.

US-made ammunition is loaded on the assumption that you have a J rifle, and pressure is held down. European-made ammunition is loaded quite a bit hotter.

Jim Watson
January 7, 2006, 07:34 PM
1904 Portugese Mauser-Vergueiro was originally a 6.5x58 calibre used by nobody but Portugal. In the 1930s-40s some, many or most (depending on who you read) were rebored or rebarrelled to 8x57 Mauser. For a military weapon that long after the 1905 change to "S" bore it is most likely a .323" barrel and will take standard commercial and surplus 8mm ammo. Most likely but not guaranteed.

Note that the 1904 Portugese M-V is not really a Mauser design or make rifle and few if any parts interchange.

Smokey Joe
January 9, 2006, 01:00 AM
P5Guy--Were I you, I'd slug my bbl, to find the EXACT diameter of bullet you need.

Vern Humphrey--I must respectfully disagree with yr statement that the bore diameter is the same. The older J-bore, adopted in 1888, is .318". When the German military changed its mind in 1905, they went with a .323" bore and called it the JS. The "S" is for "spitzer," meaning a pointed bullet. The J is a mistake, BTW--It should be "I" for "Infantry"(Or the German equivalent)--but it's a mistake over a century old, now, and there's no correcting it.

You are right in saying that there will be excessive pressure when firing a .323" bullet down a .318" bore!

Just to complicate things further, there is also a rimmed 8mm Mauser case that was intended for double rifles and the like. If in doubt whether this might be yours, checking the chamber would tell you--the space for the rim--or its absence--should be obvious, and if it isn't, any gunsmith can do a chamber cast for you which will absolutely tell. If he runs the casting material a little way up the rifle's bore, you can also tell bore diameter at the same time.

Sunray correctly describes the technique of slugging yr bbl. I would urge you, though, to use a pure-lead slug: A fishing sinker works, or a blackpowder roundball, either one, hammered to a round shape just a little larger around than your bore. A cast bullet will be a lead alloy, and be harder to shape--also harder to pound down your bbl. I've tried it with both. The cast bullet worked, but it was a PITA by comparison.

Reference: Barnes, Frank C. Cartridges of the World10th ed, 2003, Iola, WI, Krause Publications, pg. 344

Vern Humphrey
January 9, 2006, 02:05 PM
Here's what Gil Sengel says in the February, 2004 issue of "Handloader."

Most widely debated is the variance of internal barrel dimensions and bullet diameters of early 7.9mm arms and ammunition. The topic often makes use of the terms J-bore, Z-bore, S-barrel, J-bullet and S-bullet. This writer has reviwed at least eight different explanations over the years and no two are exactly alike. Let's look at a few facts and see if we can figure out what was going on.

The first fact is that bore diameter (hole reamed in the barrel before rifling) for the 7.9mm cartridge has always been 7.9mm (3.11 inch). Why some call it an 8mm is unknown. The M88 cartridge used an 8.1mm (.3189 inch) diameter bullet (J-bullet). Rifling depth for the M88 barrel was 0.1mm (.0039 inch). Simple addition now reveals that barrel groove diameter (J-bore) and bullet diameter were identical at 8.1mm.

When M88 ammuntion with its long, hard jacketed bullet pushed by the new smokeless powder was fired in these barrels, the rifling quickly wore away and barrels ruptured, split or just plain blew out in various locations near the breech. Such was not desirable. Failures were blamed on the bullet being too large in diameter, though erosive, unstable powder was more likely at fault.

As a remedy, rifling groove depth was increased from 0.1mm to 0.15mm. We now have a groove diameter of 8.2mm (0.323 inch). Neither bore nor bullet diameter were changed. These barrels had a Z stamped on them. <my note: we are still talking about the M1888 Mauser rifle> Gas leakage past the bullet stopped the barrel blow-outs and deeper rifling gave longer barrel life. Remember, Germany was after better field results from the average soldier's rifel, not smaller bench-rest groups.

When the 7.9mm S (Spitzgeschloss or pointed bullet) was adopted in 1903, its bullet was 8.2mm (0.323 inch) in diameter (S-bullet), very pointed and only 154 grains in weight. Velocity is given as 2,930 fps. Smokeless powder employed was of a type using deterrant coatings to control burning rate. Gas leakage past the bullet was no longer necessary. Bullets were shorter, which reduced jacket fouling and rifling wear.

New barrels on the strong Model 98 action rifles were chambered for the S-cartridges. Weaker Model 88 rifles having the larger Z-bore were rechambered for the S-cartridge by opening the chamber neck diameter and freeboring to further relieve pressure. These barrels received an S stamp (S-barrel). <My emphasis>.

In other words, in all but the early M88 Mausers, the groove diameter is 0.323 inches. The difference between rifles designed for the early J-bullet (or I-bullet) and the later S-bullet is in the lede, not the bore.

Smokey Joe
January 9, 2006, 02:58 PM
Vern--so now ALL "8mm Mauser" users are firing .323" bullets in .319" barrels (Except very early unaltered models)? Thx for including the quote. Yr expert has given me a headache.

8 different conflicting explanations, eh?

Sounds like good campfire argument/discussion fodder forever.

Vern Humphrey
January 9, 2006, 03:09 PM
Vern--so now ALL "8mm Mauser" users are firing .323" bullets in .319" barrels (Except very early unaltered models)? Thx for including the quote. Yr expert has given me a headache.

8 different conflicting explanations, eh?

Sounds like good campfire argument/discussion fodder forever.

The early development of smokeless powder rounds is enough to give anybody a headache.

But the short version is this -- except for early M1888 Mausers, the 8X57 (7.9X57 mm, 7.92X57mm) Mauser barrel has always been 0.323" groove diameter. Until 1903, however, it used bullets smaller than groove diameter. The change to groove diameter bullets required modification to the lede (re-throating.)

P5 Guy
January 9, 2006, 11:35 PM
Now I'm really confused!
This rifle says that its made in Germany at the Mauser plant. I don't have the rifle in front of me, but I'm sure that it says so on the receiver.
I tried the muzzle test using a S&B 8mmJS round and it looked like I expected.
Slugging is next as soon as I can.
Thanks to all for the info.

Vern Humphrey
January 10, 2006, 08:25 PM
Now I'm really confused!
This rifle says that its made in Germany at the Mauser plant. I don't have the rifle in front of me, but I'm sure that it says so on the receiver.
I tried the muzzle test using a S&B 8mmJS round and it looked like I expected.
Slugging is next as soon as I can.
Thanks to all for the info.

Your Portuguese M1904 is not an M1888, so it will have the 0.323 groove diameter if it is an 8X57mm. Since in that case it was rebarreled long after 1903, it will be for the 8mm JS round.

P5 Guy
January 11, 2006, 09:35 PM
Thanks again for all the help.

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