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MPi-KM
Posted - 11/25/2004 : 12:46:11 AM
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What is the purpose of the concave ring around the bottom (between the primer and rim) on Italian 6.5mm and 7.35mm ammo?



DocAV
Posted - 11/25/2004 : 9:07:19 PM
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In the early 1890s, when smokeless powder technology and metallurgy of cartridge cases was a "Learning Curve" situation, the initial M91 6,5 carcano caretridge case had a flat headed cartridge design. The Powder in use at the time was a very hot and erosive Nobel's powder called "Ballistite" ( double base, Nitrocellulose and nitroglycerin, very fast).
The head of the cartridge case tended to "flow" on firing ( improper hardness factor) and the primer pockets expand and allow gas escape ( Not good for the shooter).
This problem was remedied by 1895, with the introduction of one extra step in cartridsge making, the impression at the Bunting stage (heading) of a concetric ring depression, with relief headstamp) in order to get the case head hardness to a reliable level.

The inner lip of the ring also served, on firing, to "roll over" the primer edge, acting as a seal to any escaping gases.
primers on Carcano ammo were not "crimped" as was common on other (larger) cartridges used in both rifles and MGs...

by WW I, heavy crimping of Rifle cartridges became the norm , for MG use, especially for aircraft use, as loose primer cups and gas escape could jam aircraft guns wioth dire results for the Pilot who usually could not "clear" the gun efficiently whilst in the air.

The Italians maintained the idea of a "recessed headstamp " right through the history of the 6,5 and 7,35 cartridges, and also used it on the M35 8x59 Breda MG case, used in the M1914/35 FIAT, the M37 Breda, the M38 Tank Breda, and some experimental SA rifles.

As for "gas seal" ability, it seemed to work, as the problems of the first three years of use of the M91 rifle (1893-95) seemed to be solved by the addition of this deep ring to the head of the cartridge case.

It is strange though, the similar sized cartridges of the Period (
6,5x54 Greek, 6,5x53R Dutch etc, didn't have this problem, and were Fl;at based traditional design cases.

The only other case to have this grooved head was the 8x51R Lebel(French) case, but the groove was to allow the use of Pointed Bullets in tube magazine rifles ( M1898 Balle "D" and M1932 balle "N"
could be fired and loaded into the M1886/93 Tube loading Lebel rifle, without any "magazine explosion" trouble, normally encountered when pointed bullets are used in tube loaders (which usually use Flat point round nose bullets (as did the original
lebel, with its flat point "Balle M" cartridge.

The similar deep groove found on WW I and early WWII .30/06 AN-06 and AN-M2 ammo is definitely a "crimp" ring for Aircraft use ammo; the same principla was used by the French in their 7,5 MAS ammo from 1929, and in French made .30/06 (mod. 1949 Balle "O"), which ammo was predominantly for MG use, both ground and air.

Back to the Italian situation, it also made headstamp bunters easier to engrave than the traditional (impressed letter) ones used elsewhere in the world.
 
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