 Large calibre arms, such as artillery, will in general use an inert solid projectile (the proof shot); although water, sand or iron (powder) filled versions can be found for testing recoil systems.For both small arms and heavy weapons, the gun is fired remotely and then examined; if undamaged, it is assumed to be safe for normal use and a proof mark is added to the barrel.In the case of revolvers or other multi-chamber firearms, each chamber must be proof tested before the firearm may be marked.