Because of their imposing defenses, Castles are notoriously hard to penetrate, though that could also be because Frank was emotionally shattered following the punishing murder of his entire family by the mob. Or, you know, the moats with sharks in them. Giving you something even a stunted ex-Marine/moat can't stop, The Trebuchet Store.
From a US Navy Weapons Systems Engineer whose childhood interest in homemade medieval war machines resulted in an older kid getting concussed in a snowball fight, TS slings (ha!) madcap mayhem in the form of working miniature models (plus DIY blueprints/kits) of 12thC trebuchets, which, as if you didn't know, are gravity-powered siege engines that, when compared to standard catapults, represent a "quantum leap" forward, which is too bad, because the best one involves Bakula moving backward to help Buddy Holly write "Peggy Sue".
Fully assembled death-dealers include the 3ft tall solid Northern Red Oak "Bellifortis" (whose projectiles will sail up to 40ft), the smaller 2ft "War Wolf" with a range of 35ft, and a 14-incher inspired by the creations of Leonardo da Vinci that features an empty counterweight to which you can add weight for increased range, though, to be fair, that didn't work for Val Kilmer.
There's also a mess of DIY siegery that features easy-to-build plans for trebuchets (a tennis ball/water balloon launcher recommended for science fairs) and other classic catapults like the "Roman Mangonel" (10in w/ a range of 40ft), and the PVC pipe-constructed "Statistical Catapult", something Ryan Langerhans'll achieve if he can manage to hit, like, .200 this year.
If you prefer to go ballistic, there're also plans for a crossbow-ish "Roman Ballista" that shoots projectiles at a range of up to 100ft, so no one will be able to escape Punishment, even if you're unwilling to jump the shark.