Both the Colonial Viper and the Cylon Raider mount two gun units, which produce a coherent, highly visible and relatively slow moving beam of light when fired.
The weapons are referred to as �lasers� even though this does not necessarily mean that they are true lasers (see �Laser� in the Lexicon). In the case of the Viper, there is also a reference to �laser torpedoes�, and the Cylons apparently have �bombs�, which in LP, are judged by their explosions to be �50-megon� loads. We only see the Raider firing its �beams� in LP.
Despite the above, and numerous claims to the contrary, there is no visible evidence in the series that either craft can mount external ordinance or has any other weapons but those shown. Indeed, if they could, they probably would have used them in a number of situations.
A screen shot of Viper data shows four different items under the heading �Weapons�. These are �Otron Extensions�, �Laser Controllers�, �Proton Activators�, and �Point Diverters�.
On a number of occasions, particularly in LL, there is the implication that Vipers have a finite ammunition supply that must be replenished. Starbuck�s question to Bojay about fuel and ammunition tells us that the two items are separate, as does Adama�s order to have them re-fueled and re-armed. In answer to Starbuck�s question above, he is told that the fighters of the Pegasus use Cylon ammunition.
Viper fire that misses its target does one of two things. It either disappears into the distance, or the two beams converge in a very small, dull-red flash. Cylon fire that misses explodes after a certain distance. Further supporting the suggestion that the Pegasus� Vipers use Cylon ammunition, their shots exhibit similar performance when Sheba and Bojay are firing on Apollo and Starbuck.
Viper�s can survive near misses and glancing shots. Raiders are never seen to.
Two parts of the weapons system of the Viper are the laser generators and the laser pumps. What these specifically do is not stated, but apparently both are required to fire the weapons. Removing the laser generators from the Recon Viper left it unarmed, and Starbuck�s laser pump jammed in the training exercise with Athena, forcing her to �take the shot�, which subsequently also got Starbuck.
In a deleted scene from ME, Starbuck and Apollo scan the Terran shuttle for signs of weapons, specifically looking for �Lason� or �Coralax�. Not finding any, Starbuck suggests that they may use some other form of explosive, again suggesting that Colonial and Cylon weaponry has an explosive component.
What this tells us:
Unfortunately, while telling us a great deal, there isn�t a definitive piece of information that tells us exactly what these weapons actually are. As what we are seeing contradicts the idea that the Colonials are actually using lasers, there are two possibilities remaining:
1) A directed energy weapon.
2) Ablative laser-propelled explosive projectiles.
I have outlined technologies for both possibilities. Both have merit and are supported by the canonical references. Thus, it is up to the reader to decide which is preferred.