A material dispensing assembly (100) and method of operation for converting a portable cartridge dispensing tool to a bag-type dispensing tool is provided in which the assembly includes a single piece piston (110) for advancing material though a material housing (104). The single piece piston (110) includes a substantially square-shaped receptacle (140). The assembly further includes a square shaped drive rack (112) for attaching to the piston (110) at the substantially square-shaped receptacle (140) at a connection end (128). The drive rack (112) further includes a plurality of teeth (142) located thereon. The assembly (100) further has a support (127) with a substantially square profile for receiving and supporting the drive rack (112) during operation such that the construct of the drive rack and piston (110) are prevented from rotating during operation.