One thing that always bothered me about the SG1/SGA series was the battlecruisers and glider craft they made, none of which had any weaponry that was effective against anything more than fighter sized craft.
It doesn't make any sense to me, they had how many years of off world time to steal and reverse engineer Go'uld based energy weapons, like the staves and the energy cannons mounted on wheels?
Heck if they, for some reason, couldn't reverse engineer it, then why not steal a bunch of those energy cannons and fit those on the ship, as well as railguns? they have their own power source (liquid naquadah? if I remember rightly), so it's not like they would be a drain on the ships power.
A single blast from one cannon was able to destroy the bridge and crash an Alkesh (The episode when Teal'c gets stuck in the gates memory)
If you had 20+ of those things firing at a shielded target, it would probably do some damage.