  The magnetic dipole (M1) line strength between the fine-structure levels of
the ground configurations in B-, F-, Al- and Cl-like ions are calculated for
the four elements argon, iron, molybdenum and tungsten. Systematically enlarged
multiconfiguration Dirac-Hartree-Fock~(MCDHF) wave functions are employed to
account for the interelectronic interaction with the Breit interaction included
in first-order perturbation theory. The QED corrections are evaluated to all
orders in $\alpha Z$ utilizing an effective potential approach. The calculated
line strengths are compared with the results of other theories. The M1
transition rates are reported using accurate energies from the literature.
Moreover, the lifetimes in the range of millisecond to picoseconds are
predicted including the contributions also from the transition rate due to the
E2 transition channel. The discrepancies of the predicted rates from those
available from the literature are discussed and a benchmark dataset of
theoretical lifetimes is provided to support future experiments.
