The U.S. Army has recently developed cutting edge designs for gun barrels, projectiles, and propellants that require testing. This includes measuring the internal pressure during fire. There are concerns with the current method of drilling to mount pressure transducers near the breech and chamber of the gun barrel where pressure is highest. An alternative, non-intrusive strain measurement method is introduced and discussed in the present work. This focuses on determining the feasibility and accuracy of relating tangential strain along the sidewall of a gun barrel to the drastic internal pressure rise created during combustion. A transient structural, numerical modal was created using ANSYS of a 155 mm gun barrel. The pressure gradient was derived using a method outline in IBHVG2 (Interior Ballistics of High Velocity Guns, version 2), and the model was validated using published experimental tangential strain testing data from a gun of the same caliber. The model was used to demonstrate the ideal location for strain measurement along the sidewall of the chamber. Furthermore, three different pressure ranges were simulated in the model. The behavior of the tangential strain in each case indicates a similar trend to the internal pressure rise and has oscillation due to a dominant frequency of the barrel. A method to predict internal pressure from external tangential strain was developed. The internal pressure predicted is within 4% of the pressure applied in the model. A sensitivity study was performed to determine the primary factors affecting tangential strain. The study specifically looked at material properties and geometry of the gun barrel. The thickness and elastic modulus of the gun barrel were determined the most relevant. Overall, the present work helps to understand tangential strain behavior on the sidewall of a large caliber gun barrel and provides preliminary work to establish an accurate prediction of internal pressure from external tangential strain. / Master of Science / Innovative technology for large gun systems require testing to evaluate safety and performance. The most recent designs from the U.S. Army for long range artillery require higher pressures. Currently, large gun barrels are drilled to mount pressure transducers for internal pressure testing, but the new generation of weapons require a way to measure internal pressure of the gun without introducing these high stress locations. External strain offers a means to measure displacement of the barrel caused by the internal pressure change with minimal alteration to the gun barrel. The present work focuses on modelling a large gun barrel using finite elements to understand the behavior of strain on the external surface due to internal pressure during fire. Measurements were taken near the chamber of the gun barrel model. The strain behavior is comprised of two components, a linear change due to a pressure increase and vibrations introduced due to the sharp pressure increase over a short amount of time. Three cases were evaluated at different pressure ranges and a method was developed to predict internal pressure from the tangential strain with a maximum error of 4% for all cases studied. The model also indicates that the strain results are most sensitive to a change in thickness and the elastic modulus of the gun barrel material.