In the post on the Dutch Marines playing with their mortars, Heath answered a question posed by Rivrdog thusly:
Gas Rings (obturating ring ) are what you see just making it out of the tube. They expand into the tube upon firing, but when the mortar leaves the tube they fall off.
Most mortars rely on being not-quite-as-tight-fitting to the bore as regular artillery, in order to facilitate faster loading at the expense of range and greater dispersion (dispersion not always a bad thing when attacking area-targets, vice point-targets). Flexible obturating rings do not interfere with loading and dropping, but providing some extra seal (like the piston rings in an engine) and therefore range. They can have a small effect on dispersion if they help keep the rounds oriented so as to exit the tube with the same exit geometry... but not much, and the discussion is even more boring than it is already.
Here is an example, using a Yugo inert training round. The white line about the body of the projectile is the obturating ring, made out of nylon.
Read the complete post at http://www.thedonovan.com/archives/2012/05/on_obturating_r.html
Posted
May 03 2012, 11:00 AM
by
Argghhh! The Home Of Two Of Jonah's Military Guys..