The question remains. What would my fellow lefties like to see?
Personally I would favor an older classic caliber if I could somehow get a company to make a custom run of left hand rifles. With a new modern caliber (e.g 6.5CM) I'd probably just buy a current Ruger, Tikka, Sako, etc. that's already available.
So the choices that would grab my attention would be:
257 Roberts
25-06 Remington
6.5x55 SE
7x57mm / 275 Rigby
300 H&H Magnum
35 Whelen
358 Winchester
9.3x62
Make one of those available in a left-handed Model 70 or Ruger African and I think I would be able to find room in both my budget & my safe to accommodate it.
