Welcome.
Advice-
When testing, you will generally not need more than ten rounds of each load.
Test in the same weather conditions and distance.
Make sure your cases are the same cases, fired more or less the same number of times, not mix brass, same neck tension and seating depth.
Keep records of what you do, save targets for later reference. I use a very thick spiral notebook, index cards with dates stapled therein noting, weather conditions, powder, brass, bullets, charge weight, depth to ogive, outside diameter before and after loading. Don't mix primers. Don't cut corners, and Never, Never, Never adjust more than one thing at a time, i.e. powder charge AND neck tension in the same test, because you never will know which is giving you tighter groups or wider groups. Be aware that twist rate has a good sized influence on bullet performance and accuracy. All of these are listed as my personal "I should have asked first" list.
Don't afraid to ask questions. We have all been where you are at one time (or right now) or another.
Most importantly, have fun.