This study evaluates the ability of OpenSim musculoskeletal simulations to estimate upper limb muscle activation during hammer drilling. A user study was conducted with six subjects performing different drilling tasks while varying drilling postures (horizontal - two-handed, upwards - two-handed, upwards - one-handed) and drill bit size. Body motion, external forces, and surface electromyography (sEMG) of muscle groups of the upper body were measured. Muscle activations were simulated in OpenSim using an upper limb musculoskeletal model and results were compared to the experimental data. Overall, simulated activations aligned qualitatively with EMG trends across different tasks, although quantitative agreement was limited depending on muscle and subject. The results indicate the potential of such models for early-stage ergonomic evaluations of power tools. Key challenges include scaling of muscle forces in the model, user-specific variability, and vibration effects.