Thank you for posting this, it gives us reloader's some insight on what the raw numbers actually are and how much they affect group sizes.
What your link doesn't take into account is something every 1st year target shooter is taught. Namely "dwell time".
A shooter is not a mechanical rest and the dwell time of the bullet in the bbl of the firearm affects group size more then a +/- 100fps load deviation ever could in a mechanical rest/ransom rest.
AAHHHH, They said no math!!!!!!!!!!
Great you have your 2" group @ 50yds using the op's true blue target load in his revolver staged in a ransom rest. The difference in dwell time/recoil between the inconsistent burning loads only has to cause a 1/100th" change in muzzle flip/where the end of the bbl is pointing to turn that 2" group into a 5" group @ 50yds with a 6" bbl'd 357.
This is why Live Life is absolutely correct when he says "consistency ='s accuracy".
Same felt recoil, same grip, yada-yada-yada VS POP, bang, snap