I was shooting a 3-d select for target and 3-d. I changed to 4" feathersand they they still wouldn' t group well with my muzzy' s. I think it was the foc. In my case my arrows where 26.5 because of my draw length. So my speed was around 275 -280. I went back to aluminum for more wt. and they group much better. My foc increased which made me think my feathers are now controlling my arrow flight. JERRY