NIIOMTPLABOPARMBETZHELBETRABSBOM

Abbreviations are fun, are they not, and this mouthful, beyond all doubt, is the mother of all abbreviations! According to this, it stands for (translated) Laboratory for Shuttering, Reinforcement, Concrete and Ferroconcrete Operations for Composite-monolithic and Monolithic Constructions of the Department of Technology of Building Assembly Operations of the Scientific Research Institute of the Organization for Building Mechanization and Technical Aid of the Academy of Building and Architecture of the USSR. So, despite of being 56 characters long, it still entails a fairly decent abbreviation ratio of 5.54, which is better than NOPAT's 5.2, but worse than USSR with 7.75. Come to think, Russian words tend to be longer than English ones, so the homoglot ratio probably would be even better. (Thanks, RB!)