Gunsmith Cats

Taking place in a four year period, the story centers on two young women, 19-year old Irene “Rally” Vincent and her partner, 17-year old “Minnie” May Hopkins.
Rally and May operate the titular “Gunsmith Cats” gunshop in Chicago, Illinois. Rally also works as a bounty hunter, assisted by May, which is the impetus behind many of the stories.
From Baka-Updates:
Girls, guns, and grenades! Meet Rally Vincent and Minnie May. By day, they work at the Chicago gun shop that they own. By night (or holidays or week-ends), they moonlight as a pair of bounty hunters called the Gunsmith Cats. Rally is an expert at firearms, being able to judge the condition of a gun with a glance, and being an expert marksman. Minnie May is younger and less disciplined; and has an absolute fascination with explosives. Lots of explosives. Especially big ones. Together, they form an unbeatable team; much to the consternation of the local ATF bureau. Set in the city of Chicago, this action-adventure series features a lot of gunfights, car chases, and general mayhem.