Regarding load development (not nec. in this order)...

#1 - The yardage needs to be [A] short enough that conditions are as close to nil effect on the trajectory as possible (choose a day when it is very calm), and [B] long enough such that the bullet has fully stabilized. For most, this would be between 200 and 300 yards. But IF (big if here) conditions allowed, further is better.
#2 - Ensure the bullet you are developing with will use a sufficient charge to remain stable all the way to the target (current and at the longest range you expect to shoot that load) . That ALSO includes not choosing a bullet which is marginal to the barrel twist rate (optimal is fine... even overly so - but under-stabilization from an improper twist-rate for a particular bullet length will never yield great - or consistent - results).
#3 - Consider developing a load using a set of ladder tests as a starting point. You'll shoot less, but gain more insight into where the nodes are. Then you can get more detailed with-in +- a few tenths
#4 - Chronographing is an absolute MUST. Without that data, you'll have no idea what to attribute inconsistencies to. ES and SD numbers combined with your targets are going to save you loads of time...

just my 2 cents...