Now you can call me biased, since I pretty much consider everything that came before the modern cartridge (primer-propellant-bullet, metal casing to hold it all together) immature technology. So yeah, the M1858 doesn't exactly cause me to cheer, much less the exclusion of the Mk23 or other HK stuff. Still, nice choice, I'll probably end up using the 1911s most of the time, probably supplemented with the berettas. I expect any gunslinger perk working on those as well..?
The truth is, people were murdering each other using the "immature technology" anyway.