Velocity drop during ladder test

I did a 10 round ladder test of .223 through my bolt gun and had 2 rounds in the middle drop in velocity. Is this normal. I am new to reloading but paid attention to my loads. Shooters world Precision powder Lake City 5.56 brass Sierra 77 grain TMK COAL 2.318 Starting charge 22.2 gr Final charge 24.0 gr Any help is appreciated! Fred