I'm using 300yd as my zero, (.308) at the moment and will be moving out to 600yd a 100yd at time, the 20-60x60 spotting scope i have is working fine at 300yds. The questions i have are, 1-at what point will i need more spotting scope, 2-at what point will i need a spotter, 3-what spotting scope are you using? Thanks, blue