Most of the hunters on Wild Bore Fever have large round knobs on their rifles. The setup seems to work well at running hogs.

https://www.youtube.com/watch?v=-O1BqN8K0Vs

I hated the bolt handle on a Mark X so I ground it off freehand, threaded it and machined a longer tapered tactical knob. The rifles I use where I might need a fast second shot is either a post 64 model 70 or a tang safety Ruger. Both have nicely shaped bolt knobs and require no changes for me.