Top break revolvers don't have the best reputation when it comes to frame strength. Although most guys I know who've had problems with them actually had issues with the latch, which would stretch and eventually not hold the gun closed properly. (Granted, most of those guns were cheap pocket revolvers from the early 1900s, but if even a little .38 S&W will do that, it's going to be a worse problem with a cartridge or shell with more oomph.) That's the reason most modern large caliber revolvers use a tip-out cylinder on a crane.
If you want to use a rifled barrel you could consider using custom cartridges with saboted slugs. A sabot is a shroud (usually plastic) that surrounds the actual projectile. The sabot engages the rifling in the barrel and imparts spin to the slug, then falls off of the slug after it leaves the barrel. This might not be a good idea if your character is trying to remain anonymous. Someone investigating a shooting scene may find a sabot and be able to associate it with other events.