hi buddy
i don't/cant have the luxury of chair gun pro,but i have the hawke brc
i have used the ret 12 which is similar to my mamba ret (Christmas tree)
once i put all the data in,and done the calibration as Si and Tony talk of, there is a slight difference of a yd or so ?.but i just made a mental note of it.
so you have to do the field work to make sure your cock on buddy,as i have done
also its good fun,set ya self some targets out from 10 to 45yds/mtrs and make note in relation to where there landing on the mil dots BINGO!!! as easy as that and as said before loads of fun!!!