rainbow affect? I use a 225 grain aerotip powerbelt and sight it dead on @ 100 yards and am only 4" low @ 150. Rainbow affect is when you're using a heavy bullet such as a 370+ grain bullet. Thats when you really notice the rainbow.

I used to use the 245 grain HP powerbelt with 120grains pyrodex rs and i sighted in 2" high @ 100 and was dead on out to 150 yards.