Ammo calibre

**yeti** · 05-11-2021, 05:30 PM

Apologies if this is the wrong place.
I have searched the internet for a simple way to determine a cartridge calibre but I cannot find anything straightforward so can someone explain?
Would a 20mm shell measure 20mm diameter at the base? Is the length designated from base to rim or from base to tip of projectile?
So with the examples here I guess the large one is a 30mm round and other 20mm? I know all this seems obvious but I want to check I’m getting this right.
Also, I can find code info on the internet about place of manufacture but how do you determine the rounds purpose? Flak, HE, anti tank? Please help an ammo dummy!

**Teck 147** · 05-11-2021, 07:09 PM

Measure the internal Neck Diameter and the cartridge length. With those two you'll come pretty Close to the caliber. For example 12.7x99mm

**Forest Mosquito** · 05-11-2021, 07:55 PM

Hello.
The first sleeve looks like
from 23 mm Volkov-Yartsev cannons
Second sleeve.
Sleeve 20x138mm Flak 30/38
You cannot determine the type of projectile from the sleeve.
The sleeve was universal for all types of shells.

**Teck 147** · 05-11-2021, 08:30 PM

by Forest Mosquito

The sleeve was universal for all types of shells.

That's a bit misleading isn't it? There are enough examples of identical shells with differing cartridges depending on intended use. The caliber can almost always be detirmined from the cartridge/casing (unless someones firing discarding sabot or the similar)
And to be honest... between us we didn't even manage to answer all of Yeti's questions.

A 20mm Shell casing can have a close to 20mm Base, but only if the sides are parallel.
Caliber is detirmined from projectile Diameter and cartridge length without projectile.
The difference between aircraft cannon and Flak/AA is often relatively simple, Flak needs more Powder and on the ground there's more space so flak generally has in comparison to Aircraft Cannon a longer and often wider cartridge
If the projectile was HE or Anti Tank (Armour Piercing) is anyones guess and i think (next to His(?) description of what they are) that's what the mosquito is trying to explain

**yeti** · 05-12-2021, 11:31 AM

Thought you might enjoy more photos. Bit raggy but has some nice green patina left and clear stampings. Surface find too ( someone obviously has higher standards than me

)

**vegetius** · 05-12-2021, 12:26 PM

Where are they from? What context were they found in? What Are the exact dimensions, Case mouth, Base diameter, Case length and seating band width and diameter please. Then a positive ID is possible.

For what it is worth my money is on German 13mm cannon for the MG131. Alternatively the 15mm but that is not belted rimless as far as I know.

**BlackCat1982** · 05-12-2021, 12:35 PM

P181 is the Polte Armaturen & Maschinenfabrik

**yeti** · 05-12-2021, 01:50 PM

They were found in Berlin wood. Had already been dug up so very rusty and broken therefore some measurements are rough.
Base diameter is 27mm
Circumference at band near base is 100mm
Length (approx) 140mm
Case mouth (approx) 15mm

**BlackCat1982** · 05-12-2021, 02:40 PM

2cm flak being used in ground support role then.

**vegetius** · 05-12-2021, 03:43 PM

"2 cm flak being used in ground support role then."

No sorry, the 2 Cm is either Rimless or Rebated Rimmed. The Germans did not use the belted rim design for 2 Cm. I will stick with the larger being the 15 mm with a Rimless Cartridge Case, and the smaller being a 13 mm with a Belted Rimless Case.