20x138B Finn with "20/40 T 41 3 two crossed arrows" h/s


I am on my way to SLICS with a stopover at Columbus,OH gun show. I got a lot of strange (to me) ammo, which most of you probably consider ordinary. I did not bring calipers so don’t know actual measurements. One $20 wonder (which caught my eye) is a relatively large unfired round with a headstamp: 20/40 T 41 3(next to 2 crossed arrows through a circle). It is of shinny brass with a nice blue projectile with a white rim between cartridge and projectile. I got it because it was shiny, my feminine half talking. So, what did I buy? I’ll post scans next week if I survive SLICS.


If you don’t get it identified first, I’ll have my calipers at SLICS.



This is a guess (Tailgunner’s calipers are a good idea!) but maybe a 20mm Lahti? Don’t know if they come in a “shiny” loading, though…

Hitting gunshows on the way to SLICS. Man, you’ve got me beat! Enjoy and maybe you can raise a toast in memory of the home-bound and envious.



Dave, don’t envy me too much, I had to spend 4 hours at Columbus Zoo and sit at Alladin Shriners Circus in exchange for 2 hours at a gun show.


For a picture of the 20x138mm Lahti AP-T see:




I think you nailed it! I was thinking of the 20x113(?) because of the “T” but that 20x138B’s headstamp sure seems to fit the bill for Vlad’s shiny mystery…



In artillery designation, the number after the “/” means the barrel lenght in calibers. For instance there is the 40/70 Bofors, the 20/120 Oerlikon 5TG, and so on.

Does the 20/40 designator mean that the gun this round was intended for had a 40-caliber barrel lenght? That would be 20 x 40 mm, that is 800 mm = 80 cm = 31,5 inches. It seems a little short for a 20 mm gun.


Schneider, I’d go for the year of adoption.

The “/” designation is not much used within the military if I remember right. The usually write “L70” or the like.


20/40 = 20mm case model 40
T = Tikkakoski
41 = 1941


In Spain and in Italy, if I remember well, the system Caliber/Tube lenght is still used.

Here’s a list of Spanish artillery calibers from the '80s, taken from an official manual.