Reading through it, that site doesn't really show very good evidence that McCain is bad on gun rights. They seem to have a personal gripe with him because part of his campaign reform obliquely limits their organization (527s).
Almost every vote they claimed was outrageously anti-gun had to do with the required purchase of trigger locks which they call a "tax on gunownership". Cry more. The other negative shit came from his votes on the "Kohl Amendment" and related bills, which merely shift liability in case of accidental death or injury from the gun-makers to the gun-users. The site claims this is some kind of crazy requirement to have your gun lock on at all times. It's not.
Poor McCain. Conservatives cry that he's a liberal in disguise, while the libs say he's a possum waiting to show his true insane right-wing colors. In my opinion, if both types of extremists hate your guts, you're probably right on the ball.