Anobturating ring is a ring of relatively soft material designed toobturate under pressure to form a seal. Obturating rings are often found inartillery and otherballistics applications, and similar devices are also used in other applications such asplumbing, like theolive in acompression fitting. The term "O-ring" is sometimes used to describe this kind of pressure seal.
Obturating rings are common in artillery, where the steel or cast-iron casing of the shell is too hard to practically deform to provide a tight seal for the propellant gases. An obturating ring which is calleddriving band made of a softer material is the standard solution for that problem.Mortar bombs also use obturating rings to provide a seal around the projectile.[citation needed]Recoilless rifles and some artillery use rings with a reverse impression of therifling cut in them for a tighter seal even at very low pressures.[clarification needed]
Another obturating ring may be used on sliding/falling breech-blocks from the opposite side of the chamber to provide a tight seal there if the charge is bagged andlacks a case (examples include earlyKrupp guns toRoyal Ordnance L11 toM777). The obturating ring provides the sealing that would normally be provided by acartridge case.