Traditionalist Mark Chesnutt saw his 1990 debut, Too Cold at Home, go gold, but he ended up lost in the crush of Garthmania. Now his sophomore effort, Longnecks and Short Stories, should bring him out of Brooks' shadow, if not with such strong heartbreak ballads as ''I'll Think of Something'' and ''It's Not Over,'' then certainly with the up-tempo numbers. ''Old Flames Have New Names,'' about a guy's former lovers who've suddenly become someone else's wives, is a tart and tangy bit of Western swing. And ''Bubba Shot the Jukebox,'' the very funny saga of a good ol' boy who goes nuts when a sad song comes on the record machine and commits justifiable homicide ''stopped it with one shot'' is a sure hit. As a vocalist, Chesnutt is a little too laid back: You get the feeling that a couple of these songs would become classics if performed by someone with more presence. But his earnestness and his , baritone, a friendly foghorn go a long way toward making even the occasional filler here worthwhile.