There may have been a few greatswords in the ten pound neighborhood, but it wasn't anything like normal. Bearing swords could easily get heavier than that, even two to three times heavier, but they weren't ever used - or even usable - in combat. The heaviest functional sword that I've ever personally encountered was an 8.5 pound German zweihander. Claymores typically run in the 5-6 pound range. And those are two-handed swords... even five pounds is excessively heavy for a weapon designed to be wielded with one hand. 2-3 pounds is more usual. (The 5.7 kilos - around 13 pounds - that CC lists for the Laser Goofyass Axe is utterly ridiculous.)
My broadsword, which is not made of "modern materials", but of good old-fashioned hand-forged carbon steel, just like the Vikings used to use, and modelled after a historical Viking pattern, weighs just a hair over two pounds. About the same as a loaded Glock, in other words. Most of that mass is in the pommel and guard. My broadsword's balanced fairly far forward - it's designed for cleaving mail, not for agile handling - but even still, the balance point is only about six inches in front of the guard. A more typical sword would have a balance point only a couple inches from the guard. Even with my broadsword, I have no difficulty pointing it and holding it steady one-handed. Of course, I've trained for years to handle that sword... but I assume that anyone who'd be seriously trying to use a sword-gun would have sword training at least approaching mine (though perhaps rather less common sense).
If a pistol were to be integrated into the hilt, it'd probably close to double the weight of the weapon, and all of that additional weight would be in or close to the hilt, which would have the effect of moving the balance point back several inches. I'd be more concerned about how the extra weight affected the handling of the sword than about how the forward balance affected the handling of the pistol. It'd probably help control recoil, actually, though the gun would be slower to get around. Of course, at ranges where that's a serious problem, you probably shouldn't be trying to shoot your opponent, anyway. The gun is only mightier than the sword when you're more than ten feet or so away from it.
It also occurs to me that something like a third of that aforementioned Glock's weight is the ammo. Every time you pull the trigger on your sword-gun, you're firing off part of your pommel weight. I don't want to think about how that'd affect the sword's balance and handling characteristics.
Cervantes's sword-gun is just fragging retarded. I can just see firing that thing and having the recoil kick the barrel up and the blade right back into your face...
And game-mechanic-wise, the whole discussion is pointless. Just get a fragging bayonet. There are rules in CC for them already. 50¥'ll let you turn anything with an underbarrel mount into a (Str+2)M Reach 2 pole arm. That's the same damage as a sword, better Reach (the Reach is too long, really... a bayoneted rifle's reach is closer to a regular sword's than to a greatsword or pole arm's), and you can put it on an assault rifle instead of a wussy pistol.