Reisen has most probably a Mauser M1871, (the rear band and the bayonet give it away), but it's quite sketchy. Cirno might have a M1, the artist didn't bother going into detail, though. Also hard to tell with Shanghai, it guess it's supposed to be a 47, though it has a mag curve of the 74. Tagged what I could.
kunangkuadrat said: Who's the artist that drew Yuuka and Youmu? They look awesome.
Someone up there linked to a site with all their names, albeit in Japanese. I think Yuukarin's is Chihiro and Myon's is Fu, both already have a tag on this site.
Added tags for all artists and removed incorrect ones. Some of them I could not figure out if they had danbooru tags already, though, so fix it if you know better.