Numerous studies have been published about instruments intended to quantitatively measure students' epistemic beliefs about science; however, as this researcher would discover, developing an instrument to accurately measure epistemic beliefs about physics knowledge is not always as straightforward as the literature would make it seem. Given a lack of instruments intended to measure teachers' epistemic beliefs, this researcher endeavored to develop a valid, reliable, and theoretically grounded quantitative instrument which could measure teachers' epistemic beliefs about physics knowledge. 224 preservice and in-service teachers involved in science education completed a 29-item electronic survey developed using a literature informed framework of epistemic beliefs about physics knowledge. Results were used to quantitatively analyze the reliability and validity of this developed instrument. Additionally, as part of a parallel study, 14 of these teachers were interviewed regarding their epistemic beliefs about physics knowledge using semi-structured interviews. Using exploratory factor analysis, a mathematically valid solution was found for a 14-item version of this survey; however, the factors of this solution did not align with those commonly included in epistemic beliefs literature nor was this factor solution supported by interview results. Evidence from attempts to validate this instrument, along with a lack of alignment between survey-determined epistemic profiles and interview-determined epistemic profiles for 14 teachers, showcase the problematic nature of using standardized, quantitative approaches to measure teachers' beliefs. Findings from this study suggest that educational researchers deeply consider the nuance needed for their study prior to choosing a methodological approach to measure epistemic beliefs.