When it comes to reloading ammunition, one of the main concerns should be personal safety. In addition to practicing caution while handling primers and powders, avoiding distractions during the process and being careful not to overcharge cartridges, you must also practice extreme caution when testing the rounds that you load.
Before testing any ammo, be sure you are wearing proper eye and ear protection. Also, before shooting, do a final quality control inspection on each of the rounds. Look at each one to make sure there are no obvious defects, such as bullets seated too deep, cracked casings, improper primers, etc.
Set up a solid shooting platform, such as an anchored shooting bench. This is especially important if you are testing rifle rounds. In that case, you want to use a good rifle rest or rifle bags.
If you are testing for accuracy, you will need an accurate targeting system. You can do this by using a level with you set up your target.
Start slow and then gradually pick up the pace to maintain proficiency. Use a chronograph to help you find the ideal combination of bullet and charge.
Take your time while reloading, be cautious while loading your mags, and then work your magic when you get to the firing point. However, do not rush the first two steps, so you will continue to be happy with the results you obtain at the last one.