Hi,
I have just bought a German drilling (9.3x72R and 12-ga with 2 1/2" chambers). It's about 60 years old but in excellent condition with very tight action (like new). It also has the nitro proof mark on it.
1) Does anyone know who makes good 12-ga 2 1/2" shotshells? Do I have to use shotshells that are lighter loads with lower velocity and pressure? I don't know whether a drilling like this can use regular modern shotshells. Looks like it can but how do I know?
2) Should I lengthen the chambers to 2 3/4" so that I can have a better selection of ammos? Does that lower the value of the drilling?
3) The Sellier and Bellot 9.3x72R 193-gr SP ammos have a muzzle velocity of 1952 fps. It also uses flat-point bullets. The b.c. is pretty low. I am thinking about a muzzle velocity of around 2,200 fps with 200-gr Hawk round tip bulets. Do you think it's a good idea? Anyone tried that with success?

Thanks.