Here's my earlier post on the topic:
"Some people have complained about the bullets, but those bullets, properly explained, could actually be a triumph of realism.
You want lasers instead? The lasers would have to be WAY more powerful than any laser we have now. Any contemporary laser would only punch a thin hole a short distance into ordinary steel, and only at very close range, well under a mile. No good for space battles.
You say that Caprica will have a much more potent energy source than we have now? Great! Let's use bullets instead. Magnetically accelerated to, oh, half the speed of light. That would take a huge amount of energy, which is exactly what we want. We will allow the source of the energy to remain mysterious at present.
First, there is range. A bullet that fast could be useful against a target thousands of miles away. Perfect. Then there's the size of the bullet. Imagine something roughly the size of a BB. Say, 360 bullets per pound, for ease of calculation. If the bullet travels a little over one half c, or say 100,000 miles per second, how much inertial energy does it pack? Assuming that kinetic energy is proportional to mass times speed, then one such bullet would pack the same wallop as a 500 pound projectile traveling at 2000 miles per hour. Work it out!
Possible problem: would the potential energy be released suddenly and destructively on impact, or would the bullet punch a tiny hole right through the target? Here I invite a professional physicist to contribute his/her thoughts, but I suspect that the bullet would vaporize instantly, and I am guessing that the vapor would expand rapidly enough to punch out a conical hole with a fairly large exit crater, several inches across at least, as it pushed the volatilized resistance mass of the target ahead of it. Pretty destructive. Benefit? The "Rambo Effect" is actually realized. (The RE occurs when a single Huey shoots enough bullets to destroy an entire prison facility, even though in real life it would take at least a C130, maybe two, to lift that much ammunition into the air.) If a Viper fired these bullets at a leisurely 60 rounds per second, or 3600 per minute, that's only ten pounds per minute. Give the Viper a 600 pound ammo tank and the pilot can squeeze the trigger for a solid hour without letting up. That should be enough. That also explains how the Galactica can shoot a solid curtain of bullets for as long as it did escaping Ragnor, without depleting its reserves appreciably, even if the Galactica's heavy weapons shot a much more massive bullet."
