Billinghurst .50 underhammer target rifle

[Gunlaker]

Hi,

What bullet type would likely be used in a .50 cal Billinghurst target rifle? Would it likely be a picket bullet?

I'm having some pictures sent over of a rifle that's being sold on consignment. I don't have a lot of details other than it's a .50 cal underhammer with a heavy barrel, false muzzle, and a 2x WM. Malcolm scope.

thanks,

Chris.