Was doing a bit of pellet testing (Air arms field 8.44 vs JSB express 7.87) and decided that the more you practice, the more complex springers get.

Each test was done 3 times in groups of 5.
Initially both pellets were making ragged 10-15mm groups, both to the left of the aim point. Which is larger than I expected at 18 yards (length of my garden).
Then I remembered I had just added some weight to the butt pad, so maybe I need to adjust my hold. I moved my non-trigger hand back about 2cm. JSB's now a 5-6mm group bang on the aim point (except for one I pulled). Air arms now a 6-8mm group half a mil dot under the aim point.

Someone cleverer than me will tell me its about barrel or rifle harmonics/vibrations and different starting pressures of the pellets. All I know is that for each pellet I test in the future, I will have to test with multiple hold points. I don't think the sample packs are going to be big enough any more!

How much detail do other people go into when setting up/testing their springers?