Aren't Gringo 40's...actually 40mm? Knuckleduster are not 40mm miniatures. Are you trying to match the two? Knuckleduster is available in a number of scales, since the masters are digital sculpted. You have "classic" 25-28....larger 28-32 and I think he does some train scales as well.
PS: I'm about to order some of the mounted figures (or wait for their Kickstarter, not sure), but I don't have any at the moment to show you/compare.