A proof test is a form of stress test to demonstrate the fitness of a load-bearing structure, or rescue strop. An individual proof test may apply only to the unit tested, such a structure is often subjected to loads above that expected in actual use, demonstrating safety and design margin. Proof testing is nominally a nondestructive test, particularly if both design margins and test levels are well-chosen, however, unit failures are by definition considered to have been destroyed for their originally-intended use and load levels. Proof tests may be performed before a new design or unit is allowed to service, or perform additional uses. Cranes and derricks are proof tested when called on for potentially dangerous load levels or high-valued cargoes, similarly, items which are smaller and more common are nevertheless in the load path and a failure risk if not tested. Testing generally involves lifting weight or drawing tension equal to or greater than design levels, an overspeed proof test involves physically running the machine at high speed up to the test speed. This may be done during manufacture as a proof test. Physical overspeed tests may be undertaken on some machines to verify operation of the overspeed protection systems. Operation at speeds above the operating speed can greatly increase stress levels in rotating parts. Failing flywheels, rotors, etc. may present a risk in case of a failure. Historically, swords would be tested by impact before issuance- the British test. Vessels which may be a risk, such as utility-scale water towers, chemical-handling equipment, or very-high-pressure storage tanks. Rocket stage tankage, being high-valued and often the primary structure, are proof-tested when redesigned. Testing involves exposure to higher pressures than design levels, or in some cases. A firearms chamber and barrel become pressure vessels for brief periods, in firearm terminology, a proof test is a test wherein a deliberately over-pressured round is fired from a firearm in order to verify that the firearm is not defective and will not explode on firing. The firearm is inspected after the test, and if it is found to be in sound condition, in many jurisdictions a proof test and valid proof mark are required for the sale of firearms. A proof round is an assembly designed to be used in proof testing, this can use a fixed cartridge. A proof shot is a special projectile used in a round or other projectile weapons
Catastrophically burst barrel of a muzzle loader pistol replica. During proofing the barrel was loaded with nitrocellulose powder instead of black powder. The barrel was not able to withstand the higher pressures of the modern propellant.
Airsoft gun with German F proof mark and sign from the Firearms Testing Commission Suhl
German definitive smokeless powder proof marks (eagle over N figure) issued by the Beschussamt Ulm C.I.P. accredited Proof House (antlers figure) on a Walther PPS pistol.