If I remember correctly, my B30-1 .22 has a barrel OD of 18mm. I currently have the BAM 3-9x40 scope and one piece mount that I bought with the rifle, as a package deal from BAM.
I'm thinking about installing a Leapers 3-9x50 and Uniflame Industries one piece mount on it, because I like the one on my R9 so much.
That said, I haven't had any problems with the factory scope or mount on my B30. I just think the extra scope and mount that I have will be more useful on the B30 than on my B40.