All milrurp converted to hunting carbines get to keep original caliber. You are thinking about BFONG and less lethal conversions here. BFONG pistols are usually 9mm and up for whatever reason. Proper caliber blanks do exist but manufacturers still re-chamber some commercial BFONGs to 9, 10, even 11 mm. Than again, Molot AK BFONGs usually come in original caliber while TT comes in 10mm, same caliber as less lethal TT's. Less lethal stuff gets larger calibers in order to increase stopping power of a rubber bullet. Maybe that's the reason, so they just get to use the same machinery to convert real deal into both classes. There is still a way to get a BFONG certificate for a weapon which uses it's original caliber but big companies re-chamber some models while releasing other models in original caliber. Only smaller companies and private parties go for original calibers, for the most part. Maybe it also has something to do with the fact that reenactors are only allowed to use BFONG during events back in the old country, unlike us or people in the US. We just use real deal and shoot blank rounds.