Only 2.5 feet at 300 yards? Surprising (to me) I would have guessed about twice that. Too lazy to google ballistics on this though. So, I’ll take your word for it :)
That is in reference to the Hornady Leverevolution load, which has a spitzer tip and higher velocities. The standard loads have much more drop.
I have a couple of Trapdoors and getting low pressure ammunition for them is expensive. Reloading is also a trick, as low pressure loadings require much softer brass in order to seal the neck.
For a modern brush gun, I carry a Marlin .444.