Die used was an RCBS .223 Rem for crimping. I also backed it off to seat without crimping. The other die used was Lee Dead Length seating die. It does not crimp at all.
Results were that the uncrimped rounds regardless of die used grouped under .5 MOA for 10 groups of each shot. The crimped rounds grouped and average of .95 MOA with the smallest of 10 groups being .85 MOA.
I too have tested rounds crimped with the seating die. My results were worse than yours. Crimping with the seating die was a no go for me. The LFCD however is GTG in my semi-autos, helps secure the bullet and increases accuracy. YMMV