Anonymous
I would guess that your handload would behave differently. You would get probably higher muzzle speed in the carabine. If you would try to shoot the same load from a 2 inches barrel, as they did in the test, the speed would be lower (can’t guess how much lower) and you would get a big flash because the powder would continue to burn after the bullet left the barrel.
I don’t know what length of barrel ammo manufacturers use when they test the muzzle speed for their cartridges. Probably that’s the length they optimize for.