A gun is not out of proof due to wall thickness. It will me if the barrel is enlarged or the chambers are altered from say 2 1/2 to 2 3/4. Wall thickness does not mean a barrel can not be submitted for rep roof. Just that thin barrels may be more likely to fail proof or easier to dent. Below recommend wall thickness is a warning flag but you can shoot thin barrels. Just do so after a complete evaluation of the risk. I have several thin barreled guns but the only ones I shoot have the thin areas 20+ from the chamber areas