In regard to the ring jumping, I think the reduction of linkage flux isn’t caused to reduction forces; because the mutual forces between bobbin windings and metallic ring is proportional to rating of system leakage flux. Indeed the metallic ring prefer to move toward place where the less linkage flux is linked it (according to lens’s law), also without leakage flux, that different linkage flux region is not occurred. For transformer winding forces you can refer to related text similar to following handbook The J & P Transformer Book Twelfth edition A PRACTICAL TECHNOLOGY OF THE POWER TRANSFORMER Martin J. Heathcote, CEng, FIEE Newnes OXFORD BOSTON JOHANNESBURG MELBOURNE NEW DELHI SINGAPORE Page 232 of this transformer book is here The precise magnitude of the short-circuit forces depends very much upon the leakage flux pattern, and the leakage flux pattern also determines such important parameters as the leakage reactance and the magnitude of the stray losses. Manufacturers nowadays have computer programs based on finite element analysis which enable them to accurately determine the leakage flux throughout the windings. These computer programs can be very simply extended for the calculation of short-circuit forces to enable manufacturers to accurately design for these. Occasionally, however, it might be necessary to make a longhand calculation and in this case the following, which is based on an ERA Report Ref. Q/T134, ‘The measurement and Calculation of Axial Electromagnetic Forces in Concentric Transformer Windings’, by M. Waters, BSc, FIEE., and a paper with the same title published in the Proceedings of the Institution of Electrical Engineers, Vol. 10, Part II, No. 79, February 1954, will be of assistance.