I use the 36y/m zero. I shoot irons and 300m is about the limit of my middle age eyes to actually see a target well enough to hit. Which I can do consistently as my last outing proved. Using a Colt SoCOM 14.5 barrel and 55gr ball. After zeroing at 36 I readjusted slightly at 100 then moved out to 200 and 300. Biggest thing IMO is knowing your holds.