OK, I'm stumped. Shell question

[Cochise]

Ok, I thought I was pretty knowledgeable but I stumped myself.
I just came into about a box and a half of Sellier Bellot paper 12 gauge shells. I dont think that they are particularly old, maybe 30 years.
They are marked 70 on the side which I know equals 2 3/4" and have a picture of a clay target on the black & red tube.
The primers are marked SBP with 3 stars, I dont know if they are boxer or berdan.
The base is marked SBP 12 with a logo and "made in Czechoslovakia.
They are roll crimped and the top wad is marked SBP 3mm. The SBP is the company, but what does 3mm equal? Is it shot size? If so what is that in terms of American sizes? Or is it some kind of dram equivalent?

 

[mikec]

According to a web search there is no 3mm shot, there is 3.05mm. Not sure if they just drop the .05mm?? The US size equivalent would be 5. Not sure if it is shot size or powder load. There are several members who grew up in Europe on the board, maybe they can chime in.

 

[GNLaFrance]

The primers are marked SBP with 3 stars, I don't know if they are Boxer or Berdan.

They are neither. Edward Boxer and Hiram Berdan designed their primer systems for centerfire rifle and handgun cartridges, not shotshells.

 

[mikec]

They are neither. Edward Boxer and Hiram Berdan designed their primer systems for centerfire rifle and handgun cartridges, not shotshells.

I have been involved with firearms for 36 years and never knew that. Probably because I have never reloaded a shotshell, nor asked about their primer types.

 

[Cochise]

not true, I have older Alcan in both brass and paper as well as paper Fiocchi hulls in 24 28 and 32 gauge that are Berdan primed.
If you disassemble a modern 209 primer it is actually a boxer cap set into an anvil. In the old days the cheap bastards (typical reloaders) used to save a few cents by decapping and repriming their 209 and 157 size primers. In our modern world thats too much trouble for anyone to bother with

 

[blackthorne]

Cut one open.