unchambered

He swung the rifle around, unchambered the shell, squeezed the trigger, sighted through the scope.

The Last Liverbeast « A Fly in Amber 2010

He slipped the clip from his big gun and unchambered the round that was in the receiver, then he emptied the cartridges out of the revolver.

Garden of Beasts Deaver, Jeffery 2004

Thus, while the long barrow is characteristic of the Stone Age, it is impossible to tell without direct examination whether it may be chambered or unchambered, or whether the burials within it may be those of burnt or of unburnt bodies.

Encyclopaedia Britannica, 11th Edition, Volume 3, Part 1, Slice 3 "Banks" to "Bassoon" Various

This is the case with all the guns, chambered as well as unchambered, excepting the 8-inch shell-gun of 63 cwt. of patterns earlier than

Ordnance Instructions for the United States Navy. 1866. Fourth edition. United States. Navy Dept. Bureau of Ordnance

The heads for the sponges of unchambered guns are to be eight inches long; and all sponge-heads intended to be covered with woollen material must be slightly tapered and secured by a thin copper hoop, fastened with copper tacks, on the inner end.

Ordnance Instructions for the United States Navy. 1866. Fourth edition. United States. Navy Dept. Bureau of Ordnance