My Pro Hunter had the little bolt handle to start with and I replaced it with the bigger round knob off of there SSG rifle. It is a available retrofit part. It worked better but still not "smooth" by any means. I had a old type S 375 that had a similar style bolt that was very slick.

I am a big Weatherby Mark V fan and use a bunch of them, all the newer Jap and USA's are very slick in operation, so I don't think it is any thing with a full diameter bolt, probably more of a manufactoring or design standpoint.