Formal acceptance of a product by the US Government is done via a DD Form250.  It is an "exchange of title or ownership" and is accomplished between the Contractor and the Procuring Agency.  This could be the Primary Contracting Officer or Administrative Contracting Officer, but typically is a Contracting Officer's Representative (COR) who quite often is an employee of the Project Manager's Office who procured the item.

However, Army Regulation 770-2, "Material Fielding", describes the roles, responsibilities, relationships, and process for passing that equipment from the MATDEV to the CAPDEV (and field units).  Its purpose is:

"This regulation assigns responsibilities and prescribes policies for the Army’s equipment fielding, distribution, allocation, transfer and transparency responsibilities. This regulation is designed to be used in conjunction with DA Pam 770 – 2. The procedures in DA Pam 770 – 2 are mandatory to execute the policies set forth in this regulation (see AR 25 – 30)."

AR700-142 has been superseded by AR770-2