Asymmetry correction for an MR read head in a magnetic recording channel employs an exponential function to correct MR read head asymmetry. The physical-health tuning means include: a plurality of bar magnets whose obverse sides are N poles and whose reverse sides are S poles, running lengthwise; wire that is non-magnetic yet electroconductive; and a shaping support material. A membrane horn switch unit includes a pair of inner support plates having an arc shape, which are installed in the outer support plate. Stud posts can be installed on single shot and pump action shotgun forends as well.