primer setback

primer setback

[′prīm·ər ′set‚bak]
(ordnance)
The backward movement of a primer cup in a cartridge case which occurs when the base of the cup is not properly supported by the bolt face or breechblock.
References in periodicals archive ?
I reminded him this difference would at least generate increased pressure resulting in back primer setback plus bulged brass and possibly a blown receiver or bolt face.