Predicting the initiation properties of explosives is challenging due to the complexities inherent in their chemical structure and thermomechanical properties, combined with variations in the testing conditions utilized for measuring reaction ignition and propagation. In this presentation, we will discuss techniques for ranking explosive sensitivity properties in the sub-shock regime, such as the historically-utilized drop weight impact test. Specifically, we will focus on sensitivity trends in explosives such as pentaerythritol tetranitrate (PETN) and erythritol tetranitrate (ETN) with systematically tuned chemical and thermophysical properties. We will also cover modifications of this experiment that allow for in situ, time resolved optical information to be collected on ignition site formation. We have found that less sensitive explosives can sometimes form local sites of initiation that quench on the timescale of these tests, which can result in inconsistent results when only sound level diagnostics are used. Finite element and hydrocode modeling of temperature generation in the drop weight test will be discussed in the context of these experimental results.