yup , they were made from late 40's to mid '50s ,its coming back to me i think the M in 151 M (B) stood for Mannlicher , the (B) designation was it was a upgraded model , i think there was a (C) as well before the Mannlicher style was abandoned
the (B) received some action upgrades and a downgraded butt plate to a plastic one , this one is still in great shape , and also has the bronze colored rear sight , rare to find if i am remembering most were shipped with either peep or ramp , both would be special ordered