In Ammunition (p192), the M34 is neither in bullets (Autopistols, ...and heavy stubbers) nor in artillery (vehicles weapons). Of course players just argue that it's just missing of the "bullets" list but since there's nothing in the errata and I find that it's a too potent weapon to get ammo as easily as for an easy stubber...

What would you think of : Small shells : 20 or 30 mm for automatic cannons in ammunition belts used with : M34 Autocannon -> rare ?

With maybe, in "Unusual Ammunition", "Antitank small shell" tungsten core, yadyada, penetration 10, Extremely Rare.

Thanks for your advice.

What would you think of : Small shells : 20 or 30 mm for automatic cannons in ammunition belts used with : M34 Autocannon -> rare ?

Ammunition for heavy weapons usually have availability a step easier than the weapon itself, so yeah , Rare.