A backflow prevention device for a plasticizing and injection screw axially movable in a plasticizing cylinder of an injection molding machine, includes a base body having a leading head portion and a trailing neck portion and formed with a channel for passage of plastic melt by the screw to an anterior screw space, whereby a check valve is disposed in the channel. These compositions can be used to provide negative-working imageable elements that can be imaged and developed to provide lithographic printing plates that have desired imaging speed, excellent run length, and shelf life without the need for a post-exposure baking step and oxygen barrier overcoat. The mounting rail is coupled to a barrel of a firearm, preferably a rifle, and provides attachment of the clamping brackets.