I was out target practicing with my son and his wheeled bow. 70 lb cam, 550 grain arrow, release, sights the whole nine yards.278 FPS. I was shooting 69 LB Treestick wood and AD arrows 650 to 810 grains in weight. At 20 yards he was touching arrows. I was shooting 3 inch groups. At 30 yards he had two inch groups while I had 6 inch groups. All my arrow weights grouped together reguardless of arrow weight. Then we let him change his 100gr FP to some of my 250 gr FP. At 20 yards arrows were still touching but 10 inches lower. At 30 yards they were 20 inches low. I shot 160 gr differant arrows with no change of grouping. Why is there such a big differance in the two types of bows.