I tested them for the shop I was shooting for when they first came out. Using ACC's in several spine ranges and a selection of fixed blade heads, all the way from 75 gn T'heads up to the big Snuffers. I didn't think they'd be worth a flip. Well, I was wrong. They worked great for the smaller heads, up to 125 grains with a 1 1/8" diamater. With the heavier, larger diameter heads, the arrows did lose some stability. The large, unvented 2-blade Magnus II heads were practically uncontrollable with them. I'd be comfortable saying you could use them with fixed blade heads up to 100 grains at 1 1/8" diameter and do well with them.