When you’re choosing skins for weapons, the BR just looks so small in your hands compared to the DMR and even the assault rifle. In Halo 4, it was about the same size as the assault rifle, but in this game, it just feels smaller.
Halo 4’s Battle Rifle was the BR85HB Heavy Barrel Service Rifle while Halo 5 has the BR85N Service Rifle. That might be the reason, but I don’t think it is.