There are some good tips above, esp. that a 3 shot group is not enough data and 50 yards is too close. Here are some things I do:
If comparing 4 loads (a, b, c, d) get 4 really nice separate targets and set them all down range and 10 of each load.
Instead of shooting all a, then all b, then all c.... a proper statistician would make a table of randomly generated letters by throwing a dice (or however you want to generate random numbers) for example: (b,d,c,c,a,d....) now shoot the a loads at the a targets, b loads at b target, in the random order.
Me, I am not that formal: I shoot a,b,c,d,a,b,c,d,a,b,c,d..... so that variables like barrel heat, my fatigue, outside temperature, wind, scope screws rattling loose, anything not related to the load is spread out amongst ALL the competitors. I put a few fouling shots down range so load a isn’t starting with a cold barrel. Pushing patches is either every shot or find a way to have each load equally starting after a patch push.
Immediately after completing my trial, I write down the date, time, range, load data... everything... assuming I might want to refer back to this data in 10 years because it’s a lot of work. I add comments like “mild recoil, I liked it” or “max load and I sure felt it” because if you have a load under max that clearly groups as good as a max load... I’d pick the gentle load every time unless hunting Cape buffalo or the like.
Rather than measure something like outside edge distance (statistically called the range, very susceptible to fliers), or doing a bunch of laborious measurements and running statistical calculations to find the standard deviation of the spread...
Hold two targets up to the sun. Center the group by eye. There are all sorts of patterns to compare, but you’ll see the load that has the most holes forming a clump. The best load will make the tightest clump and I usually consider a few fliers my bad shooting.
When you get it down to a couple loads you can’t really pick between when holding them up to the sun... well, I pick the one that was mildest or used the powder I have the most of or is most common.
To take it farther... that’s when you start shooting one shot at one target, analyzing that data, over many many days at the range and many trials. I’m not that good with a rifle but the guys that are.... impress the heck out of me.