A project on milling of organic solids is currently underway at Leeds University aimed at establishing a relationship between milling product properties and the inputs to milling, namely the feed material properties, and milling conditions. As part of this work, it was proposed to describe the milling operation using a moment-based population balance model assuming self-similar daughters, with the aim of using model parameters as one way of describing the product. This paper reports efforts to analyze Leeds' experimental data for aspirin by this approach leading to the conclusion that the assumption of self-similar daughters is not justified. An alternative model will be presented to describe what was observed.