A strong surge of purchase-mortgage business helped lift Fannie Mae and Freddie Mac production of single-family mortgage-backed securities in May, according to a new Inside The GSEs analysis. Credit characteristics in May production were relatively unchanged, however. The two GSEs securitized $65.63 billion of single-family MBS last month, a 6.8 percent increase from April’s volume. Most of the gain came from a 23.6 percent jump in purchase-mortgage business as home buying season kicked into gear. Refinance volume was up slightly, and neither ... [Includes two data charts.]