I do not own a HW77, but have HW97K in .22 and a HW57 in .22 and many other HW.22s over years in the past, and the Jumbo RS 13.43 grains are a go to pellet in all of them.
They are Lightish for cal but work well even out to over 40 yards. The typical 16 grain .22 area i find is a sort of...