larr...MEF stands for Maximum Expansion Factor...berger's first attempt at a dedicated varmint bullet...they were match bullets minus a step or two in jacket forming...no longer manuf'd...designed for prairie dogs,woodchucks &other rodents...the name was so confusing that eunice used to tell me she wasted half her day explaining MEF!...the replacement is called Varmint...heard it has a heavier jacket design but still is a J4 jacket as was MEF...i used to buy bunches of their seconds in match & MEF's when they had their office off camelback rd in glendale,az...neat folks...miss her...i have dropped a couple coyotes with 68grn MEF's from a 6BR but range was inside 100yds...never shot at coyotes with any .224 MEF's.