Early season March Brown adult insects are bigger than the ones that hatch into April. Even guys over 95 can spot the big dark sailboats on the flat matte glarey surface of the Mckenzie in March.
Go with size #12’s early and move to #14’s for the later part of the hatch, or when you get a tough fish in softer water use the smaller bug. We have some great weather for the March Browns coming up. Overcast and 54 degrees is ideal. When water temps creep upwards have your fly box stocked with March Brown adults, cripples and emergers.
I’ll be up in a few weeks from Ca. to pick up my new drift boat in Eugene and come to find out I get to float the McKenzie! I’ll be up day and night twisting up march brown’s till then thanks for the tip!