16 pounds is a normal weight for a 45 ACP 1911. However we sell more 18.5 pound springs then 16 pound springs. Industry standards on spring tolerance is +/- 10 percent. So a brand new 16 pound spring can range from 14.4 to 17.6 lbs. Most gun spring manufactures follow this standard. SpringCo springs hold a +/- 1 percent tolerance.
Another way to fine tune your 1911 to your specific ammo, is to use a Wolff calibration pack, to determine what weight spring runs best in your 1911.