I have had experience piking on many occasions. Dividing the weight you want (50lbs) by the weight you have (45lbs) will give you a decimal figure, lets say 1.1111. subtract 1 from it or simply take away anything to the left of the decimal leaving you with .1111. divide .1111 by 5 you get .0222. multiply this figure by the bows length which is lets say 68". 1.51
1.51 is the total inches needed to take of the bow. divide by 2 and its the inches needed to cut off each limb. Has worked for me countless times.