Battlestar Galactica (2004) - Season 1
The following weapons were used in Season 1 of Battlestar Galactica (2004):
Colonial Handgun (Revolver)
A heavily modified revolver is portrayed as the standard Colonial sidearm in both the Battlestar Galactica mini-series and the first season. The handgun consists of a Smith & Wesson Model 686 revolver housed in a futuristic shell. Among other features, the weapon has an under barrel explosive launcher (like the old LeMat "grapeshot" barrel). The handgun from the Miniseries had hardly any real functionality and was redesigned almost from scratch for Season 1 when scripts required more specific actions with the guns. After that it was redesigned again and, starting with the early second season, the original sidearms have been nearly completely replaced by the FN Five-seveN. These guns were inconvenient as they had to be disassembled before they could be reloaded.
The gun appears to have been intentionally designed to resemble the gun used by Rick Deckard in Blade Runner (probably to emphasize the realistic tone of this series, as opposed to a "future show with laser-guns"). It also notable that series star Edward James Olmos also played the mysterious police officer Gaff in Blade Runner.
Cropping up now and again is the South African Vektor CP1. The handgun is mostly seen in the hands of non-military personnel, although they appear to be issued to the security detail of President Laura Roslin (Mary McDonnell). Lee holds the pistol in "Bastille Day" (S1E03). "Boomer" is seen with the pistol in Season 1's two-part finale "Kobol's Last Gleaming, Part 1" (S1E12) and "Part 2" (S2E13).
For Season 1, the FN P90 was the main assault weapon of the Colonial Marines aboard the Galactica. The attachments for the weapons (flashlight, red dot sight) are somewhat the norm for the "real world" the only difference being the attachment of a suppressor which seems to be more for dramatic effect than anything else, though may have been used to disguise the use of PS90 semi-automatic civilian models. In later seasons, the Beretta Cx4 Storm would replace this SMG, most likely due to the P90's prominent use in several series that were airing during the series' run, notably Stargate SG-1. However, the P90 would still be used (in a more minor role) throughout the run of the series.
The L85A1 is seen in Season 1 flashbacks, notably "Act of Contrition" (S1E05), as well as in the special features of the Season 1 DVD. The weapons in the show themselves have had the SUSAT sights removed (while strangely retaining the mounting base) and have the whole lower receiver and muzzle guard painted white, indicating they may only be used for ceremonial purposes.
Mossberg 500 Bullpup
The Mossberg 500 Bullpup conversion of the classic pump shotgun is carried by the rioting prisoners on the prison ship. Presumably a law enforcement issue weapon since it is not seen in the hands of any Colonial military personnel.