Good technique to trim 2mm or 1/16inch off 2x4 (without a drop saw)
A block plane will do the job - end grain is their forte. Needs to be sharp, like you may never have seen sharp, if you have not used planes before.You'll also want to set the one you are shortening up against a scrap piece so that the plane does not tear-out as it leaves the edge of the board. Just let it stick out a millimeter or two beyond the supporting scrap.