Dynamit Nobel/Geco Proof Cartridges


#1

Dynamit Nobel made two different types of proof cartridges under the Geco brand, one identified by means of a knurled rim and another by means of a primer completely covered with black lacquer that generates a higher pressure than the previous type. Can anyone explain why two different loads were made? When was one type used instead of the other?

Regards,

Fede


#2

Fede - I cannot give an accurate time line of the various types of ID used by Dynamit A.-G. and Geco on proof cartridges, but I can tell uyou there are more variations than just two. Here are some marking variations from pistol proof loads by DAG and Geco from my collection:

Red primer seal, knurled rim, red case-mouth seal.

Red primer seal, knurled ring around case about 6 mm above the head, black case-mouth seal.
Black primer seal, kurled rim, black case-mouth seal.
Red primer seal, knurled rim, no case-mouth seal.

Knurled ring around case above the extractor-groove bevel, no primer or CM seals.
Red primer seal, knurled ring around case above extractor-groove bevel, green case-mouth seal.

Black primer seal, knurled rim, no case-mouth seal.
Black primer seal (around edge of primer only), four black radial lines equi-distant apart from edge of primer cup to edge of ring, no case-mouth seal.
Green primer seeal, knurled rim, no case-mouth seal.
Black primer and case-mouth seals, no knurled ring anywhere.
Red primer seal, four black radian lines on head, red CM seal, no knurled ring.
Black primer seal (entire primer), 4 radial black lines, knurled rim, no CM seal.
Black primer seal, knurled ring around case above extractor-groove bevel,
black case-mouth seal.
Red primer seal, four black radial lines on head, no knurled ring and no CM seal.
Red primer seal around edge of primer only, knurled rim, no CM seal.

The separation from groups is by the only four calibers I bother to check, which are from top down, 6.35 mm, 7.65 mm Browning, 9 mm Kurz, and 9 mm Parabellum.

there could be others. These are what I have.

I did not list every single round by headstamp - only the different ways that were used to identify them. Why so many differences? ¿Quién sabe?


#3

John, thanks a lot for your detailed answer; you turned my question into a much more interesting discussion about Geco proof cartridges. The true is that I was comparing two variations found in 7.65 mm Browning, I should have mentioned that.

Also, where I wrote “higher pressure” it should read “lower pressure”. To make myself clear, the “Red primer seal, knurled rim, no case-mouth seal” variation is labeled “gas pressure ca. 2340 kp/cm2” and a “Black primer and case-mouth seals, no knurled ring” variation is labeled “gas pressure ca. 2200 kp/cm2”.

Do you have any other label in this caliber?

Regards,

Fede


#4

Fede,

Would the pressure unit perhaps be kp/cm^2 rather than kp/cm^3? For those of us using the non-metric system, the values you show would be equal to 31,291 PSI and 33,282 PSI if the unit is in kp/cm^2. Does that make sense for a proof pressure in a 7.65mm Browning?

Just curious…

Dave


#5

BD - on my Geco proof boxes that use that system, it is “kp/cm2”, not “3” for both 6.35 mm and 7.65 mm Browning.

7.65 mm Brownign Auto Laufbeschußpatronen (Normal bullet) mit Überladung: Gasdruck ca. 2340 KP/cm2

6.35 mm Browning Auto Laufbeschußpatronen mit Überladung, Platzpatronen mit Hartwachsgeschoß: Gasdruck ca. 450 KP/cm2. Note: This is a scarce proof loading for 6.35 mm blanks with hard wax bullets. Even blank pistols required proofing in Germany at the time these were made, and perhaps still do.
It is the only box of this type proof load I have seen. The cartridges have a white wax bullet and an all-black-lacquered primer cup, as well as a knurled rim.

7.65 mm Parabellum Laufbeschußpatronen mit Überladung: Gasdruck ca. 3380 kp/cm2.

My other proof boxes use a different system:

6.35 mm Browning Laufbeschußpatronen mit Überladung: Gasdruck ca. 1690 bar.

9 mm Kurz Laufbeschußpatronen mit Überladung: Gasdruck ca. 1820 bar.

Fede - I hope this helps.


#6

Dave, you are right, thanks for pointing out my mistake. I’ll edit my previous post.

The pressure of the “Black primer and case-mouth seals, no knurled ring” is close to the currest medium pressure for a 7.65 mm Browning proof cartridge (30,168 PSI).

John, thanks for the extra information.

Regards,

Fede


#7

The allowed pressure for 7.65 Browning varied somewhat over time.
Before WW2 in Germany it was 1650 kg/cm^2 (kilograms per square centimeter).
Several sources from 1968 to 1992 list 1800 bar as maximum pressure. In this case proof cartridge pressure would be 2340 (30 % higher).
The next source available to me is from 2002 and lists 1600 bar. This is what CIP currently publishes, together with a proof pressure of 2080 bar. (Since using Piezo instead of crushers, proof pressure is about 25 percent above normal.)

So proof cartridges from different periods have different pressures.

Regarding “kg/cm^2” versus “bar”: they differ by about 2 percent (0.981). Bar is the unit introduced with the international SI system. Because 2 percent is less than can be reliably measured in gun pressures, in practice a conversion of 1/1 was used:
1800 kg/cm^2 = 1800 bar
For some time Megapascal was fashionable: 1800 bar = 180 MPa. In a way this was more realistic, because 1800 implies a pressure precision of 1 bar, which is an illusion in firearms pressures. But MPa was dropped.

Last not least you may encounter kp/cm^2. The kilopond (kp) is what the pound-force is in the Imperial system: the force of a mass of 1 kilogram due to gravity.
1800 kg/cm^2 = 1800 kp/cm^2