I use Gecko for general practice at 10m and 20 Yards, grouping is good with the occasional flyer, but that could be me ;-)
Have you washed a batch then put unwashed & washed over a chrono in alternate strings to see if there is any difference?
Given that Gecko are about the cheapest possible decent flat nosed pellet perhaps we should accept them for what they are - a fine pellet for the price and not expensive enough to have a flap about?
Nick