A blowout preventer (BOP) assembly includes a body portion, a bore extending through the body portion, and a ram block assembly. The ram block assembly includes a first ram block being movable into the bore and a second ram block being movable into the bore. The ram block assembly also includes inserts arranged within each of the first ram block and second ram block, the inserts being movable to change a sealing diameter of the ram block assembly, wherein each insert includes a plurality of lips extending into voids formed between adjacent inserts, respective lips being positioned along intersecting regions of adjacent inserts