Battlestar Galactica (2004)

The majjority of the weapons used throughout the Battlestar Galactica universe are, in fact, "real world" weapons with some cosmetic attachments or different names.

Smith & Wesson 686

A heavily modified Smith & Wesson K-Frame revolver (likely a 686) is portrayed as the Colonial sidearm in the mini-series. Among other features the weapon has an under barrel explosive launcher (like the old LeMat grapeshot barrel)

FN FiveseveN

From the first season on this is the standard Colonial sidearm. The major difference being the addition of an under barrel explosive launcher.

FN P90

For the mini-series and the first season this was the main assault weapon of the Colonial Marines on board 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.

Beretta CX4 Storm

From the second season onward this is the standard long gun of the Colonial Marines on board the Galactica and the Pegasus. The weapons themselves have various attachments including a rail system, red dot sight and flash suppressors. In addition, during the Razor movie the weapon seems to be capable of full auto or burst fire, something the real world CX4 Storm cannot do.