Yes, heavier bullets will shoot higher. My own conversion is on a Pietta 1860 Colt style and with sights perfectly zeroed for the round ball I found the common 250 grain .45 Colt loads shot about 8" high at 25 yards and a pretty scattered group as well. With 200 grain bullets it shot only about 2" high and a much better group. There are several commercial bullet caster who offer .45 caliber bullets as light as 160 grains for the cowboy shooters and those will likely group right in there with roundballs. But, assuming your ROA has adjustable sights you will have no trouble zeroing the 200 grain bullets, it's only the 250+ weight bullets that are a problem.